What is a sleeping bag liner, and how do you choose one?

by | Nov 16, 2022 | Gear

This post may contain affiliate links.

Sleeping bag liners are an optional piece of sleep gear that can be added to a sleeping bag. They basically look like a thin sheet of fabric in the same shape of a sleeping bag so that they can fit right inside.

Once placed inside your sleeping bag, you can get in and go to sleep as usual. Sounds simple enough, right?

Okay, but what is a sleeping bag used for, exactly?

A sleeping bag liner on the floor.

If you already have a sleeping bag, you’re probably wondering why in the world would you need to add a liner. Good question! To sum it up, liners serve two main purposes:

  1. Increase the warmth of the bag
  2. Protect the bag from dirt and body oils

In most cases, liners are used for warmth. They’re actually a great solution to making your existing sleeping bag warmer without having to actually upgrade to a new one based on temperature rating.

Liners are made with a variety of different fabrics according to how warm (or cool) it needs to be. Most come in a standard size without a hood section so they’re flexible enough to use with almost any sleeping bag.

Do sleeping bag liners really add warmth?

Sleeping in a sleeping bag in the winter.

Yes! But it depends on the brand and material. For instance, some brands claim that their liners can add up to 32°F (18°C) of warmth to your bag.

So, if you had a three-season sleeping bag rated for temperatures as low as 40°F (4°C), adding a liner would theoretically make it warm enough to use in temperatures below freezing.

Now, you can’t always take these claims at face value. There are other factors such as what kind of insulation your bag has, what you’ll be wearing to bed, and how cold you personally sleep that will affect how warm you actually feel.

It’s best to put your liner to the test by using it in mildly cold or cool conditions rather than using it at temperatures that are at its limit. This will give you a better idea of what to expect and whether or not you need to layer up or even upgrade your sleeping bag to a warmer one.

Sleeping bag liner material types from coolest to warmest

Black polyester material.

Nylon and polyester liners are typically the lightest and thinnest. They’re designed to wick moisture away from your body and be breathable to help keep you cool and dry in summer weather.

Silk liners are very lightweight and can be used in summer weather or inside a mummy bag to increase the warmth without adding bulk. They don’t wick moisture as well as nylon and polyester, however.

Cotton liners are a little on the heavier side and won’t wick moisture away from your body as well. They’re not the best in terms of adding warmth, but they’re a good choice if you’re on a budget.

Down fill is an option in some liners (sometimes combined with cotton) and is one of the warmest materials available. Keep in mind that down fill does require special care to keep it from getting wet and losing its insulating properties.

Fleece liners are the heaviest but warmest type of liner. They’re often used in cold weather or as an extra layer inside a mummy bag.

Synthetic insulated liners (like ThermoLite) are also quite warm but more expensive. They’re usually made with hollow-core fibres that trap heat in a similar way to down.

Sleeping bag liner shapes

Many brands make liners in a a variety of different shapes—similar to sleeping bags. So, if you have a mummy-shaped sleeping bag, you may want to consider a mummy-shaped liner to get a more snug fit.

However, rectangular or even square liners are often more versatile because you can use them in any type of sleeping bag. You may just have a little extra fabric around your feet if you’re using it in a mummy bag.

Some brands also make semi-rectangular liners that are tapered at the feet to reduce excess fabric. These can be a good middle ground if you want more of a fitted liner but don’t want to go for a true mummy shape.

What sleeping bag liner is best?

There are tons of options out there at a variety of different price points, but Elise and I are big fans of Sea to Summit’s line of sleeping bag liners. In fact, we’ve had so much success with them that we wouldn’t use anything else.

The Sea to Summit original Reactor sleeping bag liner.

We regularly camp in the shoulder seasons (spring and fall) and even in the winter in temperatures as low as -31°F (-35°C), so we take warmth very seriously!

Liners for warm weather

These liners are best for camping in the summer. They may add a very small boost of warmth, but don’t count on that to make up for a sleeping bag that’s lacking.

Adaptor Coolmax

“Coolmax” is a type of polyester fabric that’s designed to wick moisture away from your body and keep you cool. It’s often used in sportswear for this reason.

The Sea to Summit Adaptor Coolmax weighs just 280 grams and comes in two shapes—mummy and rectangle. Since it’s a summer liner, you also have the option of getting it with built-in Insect Shield, which helps keep mosquitos away.

Best for: Camping in hot and humid weather.

Premium Silk

This silk liner is made with high quality ripstop silk with a little bit of stretch and a few degrees of added warmth, making it ideal for staying warm in summer weather when temperatures are a bit cooler at night.

It packs down small and weighs just about 130 grams.

Best for: Ultralight backpacking.

Premium Blend Silk/Cotton

This liner is made from 70% cotton and 30% silk, making it feel like you’re sleeping in cozy bedsheets with a high thread count. It’s just 160 grams, so it’s great for ultralight backpackers and campers.

However, it’s more for comfort and may not add much warmth to your sleeping bag.

Best for: Sleeping comfortably in a sleeping bag that’s already quite warm on its own.


The Expander is made with a polyester and cotton so it stretches nicely, plus down fill for added warmth. In fact, it’s designed to stretch to twice its width to help accommodate different sleep positions.

Unfortunately, it’s a bit on the heavier side at 340 grams, so it may not be the most ideal option for ultralight camping or backpacking.

Best for: People who move around a lot at night and need lots of extra room.

Liners for cold weather

These liners are best for shoulder season and winter camping because they’re focused on boosting the warmth factor of your existing sleeping bag.

All of Sea to Summit’s thermal liners in its Reactor series are made with ThermoLite hollow core insulation for superior warmth.


This is Sea to Summit’s original liner in its Reactor series, offering the lowest level of warmth—14°F (8°C). It’s the lightest and most compact at 247 grams.

It only comes in mummy shape.

Claims to increase warmth by: 14°F (8°C)

Reactor Compact Plus+ (Women’s)

For women who typically sleep colder than men, Sea to Summit’s women’s version of its original Reactor liner adds a boost of warmth in the foot and torso sections.

It’s a little heavier at 263 grams, but it’s warmer—adding 20°F (11°C) to an existing bag. It’s also mummy-shaped with a toe box and draw cord for the hood.

Claims to increase warmth by: 20°F (11°C)

Reactor Extreme

The Extreme version of the Reactor is for campers who plan to sleep in much colder conditions (or with a colder sleeping bag), featuring heavier ThermoLite insulation for an added 25°F (15°C) of potential warmth.

Since it’s heavier, it weighs in at 396 grams. It’s also mummy-shaped with a toe box and draw cord for the hood, and it also comes in a long version for tall people.

Claims to increase warmth by: 25°F (15°C)

Reactor Fleece

This is the warmest liner of Sea to Summit’s Reactor series, and probably one of the warmest liners available on the market. In addition to ThermoLite insulation, it also includes fleece in its outer material to help boost the warmth of your sleeping bag by up to 32°F (18°C).

It weighs in at 380 grams and like the others, it’s mummy-shaped with a toe box and draw cord for the hood.

Claims to increase warmth by: 32°F (18°C)

Our most used liner is the original Reactor

The Sea to Summit original Reactor sleeping bag liner in its stuff sack.

Both Elise and I find that the original Reactor is enough to help keep us warm when camping in the shoulder seasons. Elise has a three-season down sleeping bag rated for sleeping in temperatures down to 23°F (-5°C) and I have a three-season down quilt rated for 32°F (0°C).

We use the original Reactor when camping in temperatures anywhere down to about 30°F (-1°C). Once the nighttime temperatures start dipping much farther—like 27°F (-3°C) and lower—we bring our winter sleeping bags instead, which are rated for use in temperatures as low as -22°F (-30°C).

How to choose a sleeping bag liner

A woman setting up her sleeping bag in her tent at camp.

There are tons of options out there, we know. But we hope we gave you some good information and recommendations based on the brand we use and trust.

With that said, it’s important to consider your own needs and budget. When shopping for a sleeping bag liner, ask yourself these questions:

Do you need a liner for warm or cold weather? Different fabrics and insulation materials offer different levels of warmth. Choose according to the climate you’ll be using it in and your personal preferences.

How warm is your existing sleeping bag? You may need a warmer liner if your sleeping bag’s temperature rating is for 32°F (0°C) or higher.

What shape do you want? Do you want a fitted liner or one that’s more versatile? Keep in mind that mummy-shaped liners typically weigh less and pack down smaller.

What size do you need? Most liners come in a standard size that will fit most people. However, some brands offer different sizes for taller or shorter sleepers.

Do you want extra features? Some liners have zippers down the side or middle (like sleeping bags do) and some don’t. Others have toe boxes, hoods with draw cords, and even pockets.

How lightweight and compact do you need it to be? If you’re planning on backpacking, you’ll want to consider how much your liner weighs and how small it packs down. The lighter and more compact, the better.

How much money are you willing to spend? Liners range in price from around $20 to $200+. As with most outdoor gear, you generally get what you pay for in terms of quality and features.

Hopefully this article has helped you understand how sleeping bags benefit you and how to go about choosing one that best suits your needs.

So next time you’re planning a camping or backpacking trip, be sure to consider bringing one along—it might just make your sleep that much more comfortable.

Sleeping bag liner FAQs

Do sleeping bag liners really keep your sleeping bag clean?

Yes—a liner places a barrier between you and your sleeping bag. Your sweat and body oils can cause the insulation in your sleeping bag to break down over time, so by using a liner you can extend the life of your bag.

After your trip, you can simply wash your liner according to the manufacturer’s instructions. You sleeping bag may only need to be aired out and not washed, which is ideal for maintaining the loft of the insulation—whether it’s down or synthetic.

Are sleeping bag liners a good idea? In other words, are they worth it?

If you get a good quality liner and pair it properly with a good quality sleeping bag, then yes, it’s a good idea. However, if you’re using a lower quality sleeping bag or liner, it might not make as much of a difference.

Are there any downsides to using a sleeping bag liner?

One of the biggest downsides of using a liner is that it’s one more thing to pack, which can add extra weight and bulk. If you’re backpacking and trying to go ultralight on your gear, deciding whether or not it’s worth it to bring a liner can be a tough call.

It can also be difficult to accurately choose a liner based on your sleeping bag and the weather conditions. For instance, you might think you need a warmer liner because your sleeping bag is rated for 23°F (-5°C), but if the nighttime temperatures are actually in the mid-30s (1-2°C) you might find that your bag is plenty warm without the extra layer.

On the other hand, if it’s colder than expected and you didn’t bring a liner, you might find yourself shivering all night.

Bottom line: Use your best judgment and don’t forget to pack a sleeping bag liner if there’s even a chance you’ll need it.

What’s the difference between a sleeping bag liner and a travel sheet?

These terms are often used interchangeably. In most cases, sleeping bag liners are typically mummy-shaped to fit snugly inside a sleeping bag, while travel sheets are usually more of a rectangular shape.

Second, sleeping bag liners are often used to provide warmth—they’re typically made with insulating fabrics like fleece or down. Travel sheets, on the other hand, are usually made from thinner, more breathable fabrics like cotton or silk and are primarily used to protect your sleeping bag from dirt and grime.

That said, some travel sheets are made with insulating fabrics like fleece or down. And some sleeping bag liners are simply meant to provide a barrier between you and your sleeping bag (i.e. they’re not necessarily warmer than using a sleeping bag alone).

At the end of the day, it’s really up to you what you want to use—both will protect your sleeping bag and keep it clean.

Up next: Find out how to insulate your air mattress and make your tent warmer without electricity.

Popular posts

About Us

Elise & Ross

We’re Elise and Ross, avid backcountry campers and outdoor adventurers! We started Gone Camping Again as a way to share our knowledge and experience about wilderness living and travel. Our hope is that we inspire you to get outside and enjoy all that nature has to offer!

Read more about our story.