Category Archives: sleeping bag

Check & Pack

Checking and packing your sleeping bag

“Speaking of sleeping bags, has anything ever had a less creative name?” Adam Carolla

Sleeping bags are relatively quick to check and pack. First, make sure that your sleeping bag is clean and dry and doesn’t have any damage to the material. Check by running your hands over the material and doing a visual inspection. Also, check that the zippers can open and close smoothly, and any other toggles or clips are working too.

Check that the sleeping bag rating is suitable for your trip.

Next, find a clean open area at home to pack your sleeping bag. Some people find sitting or kneeling is a comfortable position to pack the bag, but the most important thing is to be relaxed and not straining shoulders or arms.

Most shop-bought sleeping bags come with a stuff sack or compression sack that makes it easy to reduce the sleeping bag volume with drawcords on the side. Generally, sleeping bags made with down compress into a smaller volume than synthetic bags (although sleeping bag technology has been steadily improving with new materials on the market each year, so it’s worth keeping an eye out for new products).

It’s really important to pack your sleeping bag in a way that minimises the risk of it getting wet. Your sleeping bag is your primary source of warmth at night and will not effectively insulate when wet [1]Hawks, Leona K., “Care of Down and Synthetic Sleeping Bags” (1990). All Archived Publications. Paper 210. Sleeping bag stuff sacks are generally water resistant, can let water in, particularly in heavy rain or if the pack is submerged. Another option is to pack the compression sack into an additional dry bag, or double bag it with garbage bags, ensuring to twist and tie the tops to prevent water getting in. Lining the stuff sack with a large plastic bag, before stuffing the sleeping bag – then twisting the plastic bag closed before sealing the stuff sack is a good way of adding an extra layer of protection from water.

There are two ways to pack a sleeping bag: rolling or stuffing. Generally, stuffing is a good option if you have a compression bag and you want to get the sleeping bag as compact as possible. Rolling is very straightforward, but results in a larger volume bag so is generally used in situations where volume doesn’t matter (e.g. car camping).

Option 1: Stuffing (generally for down sleeping bags)

Start at the foot end of the sleeping bag and place it into the bottom of the stuff sack (this lets the air escape through the top of the bag). Then gradually add small wads of material into the stuff sack without folding or rolling the bag. The aim is to fold the material in a random (and different) way each time you stuff the sack, and in doing so, this keeps the insulation in the sleeping bag evenly distributed and performing better over time. It also reduces lumps in the fabric and likelihood of tears on the material.

Tighten the cord at the top of the compression sack, and then adjust the straps on the side to reduce the volume further. Tighten the straps little by little, keeping the compression even across the sack.

Option 2: Rolling (generally for synthetic sleeping bags and when volume is not an issue)
Lay the sleeping bag out on the floor and fold the sides in to create the desired roll width. For some sleeping bags, this will be thirds, others halves. Decide based on the what width you need the final roll to be.

Then begin to roll up the bag from the foot end, keeping the roll as tight as possible. For extra pressure, you can place a knee on the roll. Once entirely rolled, tie up straps, or use tape or rope to prevent the bag from unrolling. Sometimes it can help to grab another person to give you a hand attaching the straps.

References   [ + ]

1. Hawks, Leona K., “Care of Down and Synthetic Sleeping Bags” (1990). All Archived Publications. Paper 210

Use in the field

Using your sleeping bag in the bush

“Good people are good people because they’ve come to wisdom through failure.” William Saroyan

Insulation in sleeping bags works best when it is all ‘fluffed up’ and fully expanded. Once your shelter is set up, unpack your sleeping bag and give it a few shakes to get the expanding started.

Sleeping bags work best and last longest when kept clean and dry, so in the field, try to minimise the amount of dirt, sweat and dust that gets onto the bag [1]Hawks, Leona K., “Care of Down and Synthetic Sleeping Bags” (1990). All Archived Publications. Paper 210 URL = https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1209&context=extension_histall. Air your bag out after each use (in the morning over breakfast before packing up is best) – avoid direct contact with UV light for extended periods of time, but an hour of sunlight can help kill smell causing bacterial and fungal growth[2]Amichai B, Et.Al.,“The efficacy of sun exposure for reducing fungal contamination in used clothes.” (2014). Isr Med Assoc J. https://www.ncbi.nlm.nih.gov/pubmed/25167689.

Treat your sleeping bag gently! Bags that are well cared for will stay warm for longer [3]Hawks, Leona K., “Care of Down and Synthetic Sleeping Bags” (1990). All Archived Publications. Paper 210 URL = https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1209&context=extension_histall. Do not use a good sleeping bag near the fire. All it takes is a single glowing ember from the fire to create a hole and damage the bag. Not to mention all the dirt, dusk and smokey smell that the bag will pick up. If you like having something to wrap around you at the fire, consider a lightweight fireproof thermal shawl or throw over instead.

A sleeping bag liner is a very worthwhile investment. Not only does it keep your sleeping bag clean and dry, but it provides extra warmth. Avoid sleeping in your bushwalking clothes overnight. Instead, change into nighttime camp clothes. This reduces body odour transferring to the sleeping bag and minimises the amount of oils or body sweat.

A few extra tips

  • Give your bag a chance to fluff up especially on colder nights.
  • If you are too hot in the bag, try un zipping it part way, take your head out of the hood or shake the bag to force out the warmer air.
  • Try to minimise the amount of direct contact that your sleeping bag has with the ground. Use a ground-sheet if sleeping in the open, to protect sleeping pad and bag.
  • When airing out your sleeping bag, hang it high off the ground, to reduce the chance of the bag getting dirty.
  • Never force any zippers or buckles if they get stuck. Instead, be gentle and slowly undo any caught fabric.
  • If using a sleeping bag without a hood, wear a hat or hoodie to keep warm and reduce the mozzies (if the shelter does not have a flyscreen).
  • Wear clean clothes and be clean when getting into your sleeping bag.

Tips and tricks if you are feeling cold in your sleeping bag
If you are feeling cold then here are some tips to help

  • Fully zip up your bag and use the hood.
  • Ensure your insulation in your bag is inflated and evenly spread over the top of you.
  • If rolling around, try to keep the bag from moving.
  • Reduces air flow around the bag – block any drafts.
  • Especially if you feel cold between you and ground than improve the insulation of your pad. Add clothing (or even your pack) between you sleeping pad and ground.
  • Use a sleeping bag liner as this can increase temperature by up to 5 ℃.
  • Wear a beanie to keep the head warm and loose fitting layer of warm clothes.
  • Place your head inside your sleeping bag and breath inside the bag for about half a minute to warm up the air. Be mindful that your breath is also humid, so avoid doing this for long stretches as condensation inside your sleeping bag can be counterproductive.
  • In an emergency scenario, you can use a foil wrap from your first aid kit for warmth. Be mindful again for condensation and water collecting on the foil and wetting your bag.

Sleeping with or without clothes on
There’s a lot of debate around whether or not wearing additional layers of clothing adds more warmth to the sleep system or detracts, with strong advocates on both sides and surprisingly little research on the topic.

A blogger called ‘onlinecaveman’ frustrated by the lack of information carried out his own DIY experiment to test the difference between heat loss wearing a layer of clothing versus not wearing a layer of clothing. He found that the system that used a layer of clothing lost less heat than the one with no clothing.

The main purpose of a sleeping bag is to create a layer of warm air around the body by trapping body heat, so any additional layers may enhance this effect. Sleep systems work best when the insulation is allowed to do its job, that is, the insulation isn’t overly compressed (i.e. too many clothes).

It seems the layering effect that we use with clothes during the day also works in the sleeping bag, however, avoid tight-fitting clothes (these can restrict circulation), and ensure extra layers are clean and dry. Also stay away from clothes with zippers or other hard or patterned sections that may cause pressure sores.

References   [ + ]

1, 3. Hawks, Leona K., “Care of Down and Synthetic Sleeping Bags” (1990). All Archived Publications. Paper 210 URL = https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1209&context=extension_histall
2. Amichai B, Et.Al.,“The efficacy of sun exposure for reducing fungal contamination in used clothes.” (2014). Isr Med Assoc J. https://www.ncbi.nlm.nih.gov/pubmed/25167689

Care & Maintenance

Looking after your sleeping bag

“A good laugh and a long sleep are the two best cures for anything.” Author unknown

Sleeping bags can be used for several years before they need a wash. Washing tends to add wear and tear to the bag and reduces the loft (i.e. insulation), so if you can delay the need for washing by caring for the bag, this is the best long-term option.

Check your bag over regularly to make sure that all the zippers are working and the seams are intact. Check that the insulation is evenly distributed as over time the insulation can clump unevenly (suggesting that a wash might be in order).

Carry out small spot-cleaning jobs on areas such as the hood that are likely to accumulate sweat and dirt. Mix a little water with non-detergent soap to create a paste. Hold the shell away from the filling and use a toothbrush to clean and rinse the shell. By keeping the shell away from the filling you can clean the area without getting the inside wet.

When you do decide to wash it, do it as per manufacturer’s instructions.

Hawks, Leona K., “Care of Down and Synthetic Sleeping Bags” (1990) provides this table as a guideline:

Type of sleeping bagHand washMachine washDry clean
DownBest method - wash using soap and water softener

Don't use detergent - it will strip natural oils from feathers

Machine dry on low heat or no heat. Heat can burn off the natural oils
Use only if recommended by manufacturer

Wash with soap and water

Don't use detergent - it will strip natural oils

Machine dry on low heat or no heat. Heat can burn off the natural oils
Not recommended

Dry cleaning chemicals residue toxic when inhaled

Attacks down's natural oils
SyntheticGentlest method
Use detergent or soap and water softener

Washing or drying should not be above 60° Celsius
Fastest and easiest method
Use detergent or soap and water softener

Washing or drying should not be above 60° Celsius
Not recommended

Dry cleaning chemicals dissolve resin and silicone finishes used to stabilise fibers

Fibers lose crimp above 60° Celsius

In general, the process for washing a sleeping bag looks like this (but check and follow specific manufacturer’s instructions):

  1. Washing: Do up all zippers before washing to protect them.
    1. Hand washing: Fill up a large bucket or bathtub with warm water. Add a small amount of non-detergent soap. Gently massage material and leave to soak (but no more than 1 hour). Gently squeeze bag to remove any water and empty the water. Refill with clean water, massage the material to remove suds, and let the bag sit for 15 minutes. Repeat until all suds are gone.
    2. Machine wash: Many sleeping bags can be machine washed in a front-loader or a top-loader without an agitator. Add a small amount of appropriate soap (do not over-soap to ensure no suds are leftover). Consider adding a few additional wet garments to balance out the spin of the machine (e.g. t-shirts). Consider running the cycle a second time soap-free to remove all soap residue).
  2. Transferring: Take care when handling your wet sleeping bag so as not to damage the fabric. When the down is wet and heavy, it is particularly vulnerable to stretching and tearing. Take time to squeeze out as much water as possible from the bag as possible, and lift the bag from below to support the material.
  3. Drying:
    1. Dryer: Once most of the water is out of your bag place it in the dryer and use a low heat to ensure that synthetic materials do not melt. As the bag dries, the insulation tends to clump together. This can be avoided by placing objects (tennis balls or other soft but firm objects) into the dryer during the final stages of drying to displace the clumps. Once dry, air the bag out overnight to make sure there is no residual moisture before storing.
    2. Air drying: Place the bag on a clean surface outside in partial shade as UV rays can degrade synthetic materials. As the bag dries, the insulation tends to clump together, so check the bag periodically and manually break up the clumps.
  4. CAUTION: What not to do!

    • Never dry-clean your bag. The chemicals used in the dry-cleaning process can damage the bag fabric.
    • Avoid using fabric softeners or bleaching chemicals on your bag. Follow manufacturer’s instructions for what soap to use (usually a non-detergent soap).

    Other maintenance jobs:

    • Rips to fabric: If the outer layer of fabric is damaged, consider doing a small repair job by hand if it occurs in the field to prevent loss of insulation, then back home, remove stitching and do a more thorough job using gear-repair tape.
    • Leaking down feathers: Over time, a few down feathers may work their way through the outer shell fabric and poke out. Work the feathers back into the insulation layer by gently massaging the surface and pushing the feather back in.
    • Waterproofing: Some sleeping bags have a water-resistant outer layer which helps protects the bag from water damage and dirt, but eventually wears off. Consider reapplying the durable water repellent using a suitable product (check with your manufacturer).

    Storage
    Store your sleeping bag in a cool dry area away from direct sunlight. The bag is best stored fluffed up. Many sleeping bags come with a large breathable storage bag us this otherwise a cloth bag like a pillow case of larger is ideal.

Selection

Choosing your sleeping bag

“The very definition of beauty is outside.” Adam Carolla

When selecting a sleeping bag, the temperature rating, shape, insulation type and additional features such as hoods and zippers are key considerations as well as the price.

Another option for ultra lightweight bushwalkers is the overquilt or integrated sleeping bag/mat system – more details below.

Temperature Rating Selecting the appropriate sleeping bag temperature range

Sleeping bags come with a temperature rating that is a guideline for what conditions the bag is most suitable for. However, everyone is different, and some people feel the hot/cold more than others, so be prepared to adjust accordingly to find something that best suits your needs.

The temperature rating is a guideline for what temperatures the manufacturers suggest that the bag can be used in. Manufacturers generally do in-house evaluations to find the ‘R-value’ that represents the insulative properties of the bag. Some manufacturer’s use the EN 13537, which is an European standard that aims to standardize sleeping bags manufactured and sold in Europe. No such standard exists in Australia, but many sleeping bags sold in Australia do follow this EN rating system.

The EN 13537 standard rating system tests sleeping bags using a manikin. The manikin is dressed up in a layer of thermal underwear and is resting upon a sleeping pad. The testers record heat loss by the manikin to determine the extreme and comfort limits of the bag. There is a surprising amount of detail that goes into ensuring accurate thermal measurements, everything from arm positions, through to weight of the manikin [1]Kuklane, Kalev, and Valter Dejke. “Testing sleeping bags according to EN 13537: 2002: details that make the difference.” International Journal of Occupational Safety and Ergonomics 16.2 (2010): 199-216.

Sleeping bags often visually depict their thermal limits. Examples include Columbus, Mont and Sea to Summit:

Columbus


Mont


Sea to Summit

The three measurements listed as part of the rating are [2]European Committee for Standardization (CEN). Requirements for sleeping bags (Standard No. EN 13537:2002). Brussells, Belgium: CEN; 2002:

  1. Comfort rating: Defined as the lowest temperature that a standard woman can get a comfortable night’s sleep.
  2. Lower limit temperature: Defined as the lowest temperature that a standard man can still sleep throughout the night in a curled position.
  3. Extreme limit temperature: Defined as the lowest temperature that a standard woman can still survive for 6 hours without risk of death (but with a risk of hypothermia and frostbite). This is intended to be an extreme scenario where you can survive but probably will not sleep.

Sometimes a fourth temperature rating is also given – maximum temperature – that is, the hottest conditions that the bag can be used in.

Men can generally get a comfortable night’s sleep at lower temperatures than women, so the comfort rating is based on a more conservative rating for women (unless explicitly stated as ‘men’s comfort’ or ‘women’s comfort’).

For the thermal testing process, a standard man is defined as 25 years of age, weighing 73kg and at a height of 173cm. A standard women is defined as: 25 years of age, 60kg, 160cm [3]European Committee for Standardization (CEN). Requirements for sleeping bags (Standard No. EN 13537:2002). Brussells, Belgium: CEN; 2002. However, none of us are standard! Temperature is a very personal thing, and it’s important to take into account personal factors that might affect how warm or cool you sleep.

Sleeping bag rating and general fitness level can affect how warm you sleep in general, but more subtle changes such as how tired you are at the end of the day or whether or not you’ve eaten well on a trip (going to bed hungry may leave you colder than if you’ve eaten well as your metabolism is a significant source of heat production overnight) can change your sleep patterns also.

Bushwalkers that walk in NSW all year round tend to have two sleeping bags: a summer bag and a winter bag – although this will vary greatly depending on the location of the walk and the forecast. This gives them the option to use the one that is most appropriate for the conditions.

Sleeping bagApproximate monthsComments
SummerOctober-MarchOn cooler summer days, or autumn/spring period, consider carrying additional layers.
WinterApril - SeptemberOn hotter winter days, use a liner only and put your sleeping bag on top of you as a throw over (rather than wrapped tightly).

A good rule of thumb is to select a bag with a comfort rating that is 10 degrees below the ambient temperature you expect on the trip.

CAUTION:

  • Weather patterns can bring unpredictable cold spells, so it’s important to check weather conditions relative to where you plan to walk before decided on the appropriate sleeping bag. If unsure, take a warmer sleeping bag and additional warm layers.
  • At altitude (e.g. Snowy Mountains), conditions are cooler and can change rapidly. Remnant snow patches from winter time can still be seen on Mt Kosciuszko during summer months, and cold windy weather patterns can persist. Take into account these highly variable and cold temperatures when selecting a suitable sleeping bag for an alpine trip.

A last word of warning: cheaper bags may not have undergone laboratory testing, and ratings may not be accurate.

Shape Selecting the appropriate sleeping bag shape

Similar to sleeping bag liners, sleeping bags come in a few different shapes.

NameExampleImageProsCons
RectangularSummer example

Black Wolf Jardine Hodded Sleeping Bag



Winter example

Shamocamel® Sleeping Bag Envelope / Rectangular Bag -5-15°C Keep Warm Ultra Light (UL) 220 Camping Outdoor Shamocamel® Single

- Cheap
- Lots of room to move around
- Works best in warmer conditions because of loose material
- Generally heavier and bulkier because of additional material so less suited for overnight bushwalking
Semi-rectangular (or barrel-shaped)Summer example

Sea To Summit Tk I Sleeping Bag



Winter example

Sea To Summit Tk II Sleeping Bag


- This type of bag is inbetween a rectangular and mummy, so it is still quite roomy while at the same time having less air pockets to heat so is a good insulator.
- Comfortable, lots of room for shoulders and hips.
MummySummer example

Sea To Summit Micro MCII Sleeping Bag UD



Winter example

Sea To Summit Talus TsI

- Warm, body-hugging
- Very effective at insulating
- Lightweight and small volume due to less material
- Tight
- Some people find them very restrictive and uncomfortable to sleep in
- Generally pricey
Double-wideExample

Sierra Designs Backcountry Bed Duo 600 Sleeping Bag

n/a- Efficient option for couples- You probably need another single sleeping bag for trips without your partner

length Selecting the appropriate sleeping bag length

Regular and long
Sleeping bags generally come in two lengths: regular and long. It’s worth getting the right length as a bag that’s too short will leave you cold at the shoulders and neck, whereas a bag that is too big will leave your feet cold.
Check the specifications to decide on the right size by matching your height to the bag length.

Some manufacturer’s sell female bags that are designed to fit women better than the standard mummy or barrel shapes due to their shorter length, narrower shoulders and broader hips.

Half-bags
For ultra lightweight camping, half-bags are coming back into fashion (e.g. Hispar Half Bag). The logic is that the user already has enough clothing to keep their upper half warm (down jacket, thermals), so the sleeping bag only needs to be long enough to cover legs.

Hispar Half Bag

Kids sleeping bags
For people with petite build, it may be suitable to use a children’s sized sleeping bag (e.g. Coleman Kid’s Firefly Sleeping Bag). However, take care to examine temperature ratings and bag weights carefully as materials used in children’s sleeping bags are generally lower quality (and hence heavier and less insulating).

insulation Selecting the appropriate sleeping bag insulation

The insulation in a sleeping bag traps the heat your body produces while you sleep and keeps you warm.

Materials
Synthetic material and down feathers are the two main types of insulation used. For down insulation, duck or goose down (or a mix) are most common, although pure duck down is most abundant because more ducks than geese are manufactured and sold as meat, and so duck feathers are cheaper and more plentiful.

InsulationExampleProsCons
Synthetic

Sea to Summit Voyager Sleeping Bag – Vy3


  • Dries quickly

  • Can insulate when wet

  • Cheaper than down

  • Non-allergenic
  • Generally larger volume and heavier

  • Not as good at insulating (per weight) as down

Down

Sea to Summit Trek Sleeping Bag – TKI

  • Very effective insulator

  • Packs to small volume

  • Lightweight

  • Loft retains form over a long time and hence is a long lasting insulator

  • Dries slowly

  • Cannot insulate when wet

  • Expensive

Hybrid synthetic-downThese hybrid bags contain a blend of synthetic and down feathers, with pros and cons from both materials. Sometimes they are blended, in others, they are layered with synthetic materials on the bottom and down feathers on top.These hybrid bags contain a blend of synthetic and down feathers, with pros and cons from both materials. Sometimes they are blended, in others, they are layered with synthetic materials on the bottom and down feathers on top.

Down feathers are generally treated to become somewhat water resistant to some moisture, but not effective if fully immersed or soaked (i.e. down is water resistant not waterproof).

Some companies are moving towards ethically sourcing down in response to a number of issues but in particular live plucking. A few companies such as North face have put in place policies to ethically sourced down insulation and responsible auditing of all manufacturing steps including production and collection of feathers to ensure humane treatment of animals. Price alone does not tell you if the material is ethically sourced or the workers treated well.

Fill power
The fill power describes the insulation properties of the bag, or the down’s ability to loft (i.e. trap heat). It is a measure of how much air the insulating down can trap (i.e. its ‘fluffiness’), and generally speaking the higher the fill power, the more insulated the bag is. The fill power is a factor of how many cubic inches the insulation takes for each ounce. 300 is a low end feather an 900 a high end down.

Sleeping bags with a higher fill power rating are more fluffy and better insulators than lower fill power bags. For instance, the insulation in a 600 fill power sleeping bag is more fluffy and effective at trapping air than the insulation in a 400 fill power sleeping bag. Since high power insulation is a more effective insulator, manufacturers need to use less volume and thus can create lighter weight bags (including ultralight gear).

Fill power reduces over time as the bag ages and gets dirty. That’s why it pays to look after your sleeping bag to keep it as effective as possible!

Features Selecting additional sleeping bag features

At its most basic, a sleeping bag comprise of an outer layer, insulation and an inner lining, however, sleeping bags and stuff sacks do have a few additional features to consider which we’ll work through here.

Sleeping bag

  • Hood
    Hoods provide additional warmth and comfort and help retain insulation across the body. However, in warmer conditions, a hood may be overkill. Some sleeping bags come with a detachable hood (e.g. Black Wolf Zambezie King -5ºc Hood Removable Sleeping Bag) giving users the option to carry it in cooler conditions, or remove it for warmer trips. Some ultralight bags do not have a hood at all (e.g. Feathered Friends Vireo Sleeping Bag)

    Some hoods offer a pillow pocket where you can put your pillow securely inside. Others come with ‘clinch-able’ contour hood allowing users to wrap their head thoroughly (great for cold weather conditions) in the sleeping bag (or around your entire pillow also).

  • Zippers
    Most sleeping bags have one side with a zipper to provide easy access into and out of the bag. For some bags, you can specify which side you prefer the zipper on (perhaps you find it easier to exit on the left than the right): e.g. Sea To Summit Trek 2 TKII Down Sleeping Bag – Regular.

    For couples, it’s possible to zip up compatible bags to create a double bag. For rectangular sleeping bags, unzip the bags, lay them together with the insulation facing inwards and zip up corresponding zippers. See this video. For joining mummy-shaped sleeping bags, you must join a right hand zipper sleeping bag with a left hand zipper sleeping bag.

  • Pockets
    Some sleeping bag designs include pockets for valuables such as money, passports or phones. Internal pockets are preferable so that you can grab items without opening the bag and losing all the nice trapped warm air.
  • Straps
    Some sleeping bags have loops that can be used to connect the sleeping bag to sleeping pad. Also handy for hanging up sleeping bag to air.
  • Neck baffles
    Additional insulation around the neck area to prevent warm air escaping (usually only on bags designed for cool conditions).
  • Draft tube
    This is a thin insulated tube that surrounds the zipper area and prevents warm air escaping through the zip system.
  • Trapezoidal footbox
    This design adds additional space around the feet for more natural comfort during the night (particularly for those people that sleep on their back).

Stuff sack

  • Compression straps
    Compression straps make an enormous difference to reduce the pack volume of a sleeping bag. They work by compressing evenly around the stuff sack by drawing the straps downward and can reduce the volume by more than 50%.

Alternative Designs Overquilt and integrate sleeping pad

The sleeping bag, sleeping bag liner and sleeping pad system has been around for a long time with little change to the core principles: create warm space by insulating heat loss from body, particularly loss through the ground.

Recently, there have been a few new designs suggested for sleep systems that aim to optimise this setup, and ultimately save on weight.

Overquilt

An overquilt is a blanket style sleeping bag. It keeps users warm by covering the upper side of the sleeping, but not the underside (which gets compressed when you sleep on it and reduces insulation). Overquilts are often used by ultralight hikers or by hikers that use a hammock.

They are lightweight and versatile, enabling the user to adapt the bag to best suit conditions and some users report to use them exclusively over a sleeping bag. Take care when selecting an overquilt to match it to your needs, checking that there is enough insulation around the neck and head.

‘Integrated sleeping pad’, ‘pad sleeve’ or ‘hybrid sleeping bag/pads’
Another design is to integrate the sleeping pad into the sleeping bag system, creating one unit. The idea again here is to save on the weight and material of the underside of the sleeping bag that gets compressed and insulates poorly. Since the sleeping pad is doing most of the insulating anyway, this design does away with the underside of the sleeping bag altogether.

Source: https://www.gizmodo.com.au/2014/10/your-next-sleeping-bag-might-not-have-a-zipper-or-even-be-a-bag-at-all/

References   [ + ]

1. Kuklane, Kalev, and Valter Dejke. “Testing sleeping bags according to EN 13537: 2002: details that make the difference.” International Journal of Occupational Safety and Ergonomics 16.2 (2010): 199-216
2, 3. European Committee for Standardization (CEN). Requirements for sleeping bags (Standard No. EN 13537:2002). Brussells, Belgium: CEN; 2002