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Sleeping bag liner: a washable layer that protects your bag

By the Plain Prepper editors. Updated 2026-10-15.

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Quick answer

A sleeping bag liner is a washable layer you sleep inside your bag. Sea to Summit says it keeps sweat, skin oils and grit out of the insulation, so you wash the bag less and it lasts longer. Thermal liners also add warmth: Sea to Summit estimates up to 4°C (7°F) for its Reactor and up to 8°C (14°F) for its Reactor Fleece. That assumes a bag and pad already suited to the conditions. No liner makes up for a poor sleeping pad.

Why use a liner at all

• It works like a sheet. Sea to Summit compares a liner to the sheets on a bed: easier to wash than the bag itself.
• It protects the insulation. Skin oils can migrate into down or synthetic fill and stop it lofting fully, and fine sand can work through the inner fabric and wear the fill.
• It means fewer bag washes. Sea to Summit says this extends a sleeping bag's life.
• It adds comfort. Depending on fabric, a liner adds some warmth in cool weather or wicks moisture in humid weather.
• It travels. A rectangular liner with a pillow sleeve is a clean sheet for hostels or borrowed beds, and in summer a liner can be used alone.

Liner fabrics compared

Liner	Fabric	Best use	Shapes
Reactor	Stretch-knit Thermolite Pro with infrared-absorbing ceramic pigments	Adding warmth, estimated up to 4°C / 7°F	Mummy, Mummy with drawcord
Reactor Fleeceweight	Hollow-core fibers and grid fleece	The biggest warmth boost, up to 8°C / 14°F	Short, Regular, Long
Silk Blend	72% Thermolite Pro yarns, 28% silk, stretch side panels	Lowest weight and bulk; travel	Compact Mummy, Mummy, Rectangular with pillow sleeve
Breeze	70% Coolmax EcoMade, 30% Tencel Lyocell knit	Hot, humid nights; wicks moisture	Mummy with drawcord, Rectangular with pillow sleeve
Comfort Blend	Polyester and Tencel Lyocell knit	Soft moisture-wicking sheet when weight does not matter	Rectangular, Rectangular with pillow sleeve

Sea to Summit lists the Compact Mummy Silk Blend at 4.6 oz and the Compact Mummy Reactor with drawcord at 9.5 oz, so the silk blend is about half the weight.

How much warmth does a liner add?

Sea to Summit says a single number is hard to give, because so much depends on the rest of your sleep system. Its estimates, assuming a bag and pad suited to the conditions:

• Reactor: up to 4°C / 7°F
• Reactor Extreme: up to 6°C / 10°F
• Reactor Fleece: up to 8°C / 14°F

What limits the gain:

• The bag: drafts past the zipper, a loose hood, no draft collar or compressed insulation all leak heat that a liner can only partly offset.
• The pad: Sea to Summit suggests an R-value of 1 to 2 for summer, 2 to 3 for early fall, about 4 for late fall and 5 or more for winter.
• Wind and damp: moving air through mesh tent walls, humid air and damp ground all draw heat away.

Fit and getting in

• No zipper: you slide in from the top. The Reactor and Breeze mummy liners have shoulder openings for a little more room.
• Size: Sea to Summit says Compact mummy liners suit sleepers up to about 5 ft 10 in (178 cm); taller or heavier sleepers should choose the standard Mummy.
• Shape: because the knit liners stretch, they do not need to match your bag's shape.
• Drawcord footbox: on the Reactor and Breeze drawcord versions you can open the base, hitch the liner up and walk around camp at night.

Washing and storage

1. Machine wash with normal detergent. In a top-loader, put the liner in a pillowcase so the drawcord cannot snag.
2. Skip fabric softener; Sea to Summit says it reduces wicking.
3. Air dry. Dryer heat can damage the Silk Blend.
4. Make sure the liner is dry and aired before long-term storage. The Reactor liners can be kept in their stuff sack.

Sea to Summit says its liners carry no flame-retardant or PFAS treatments.

Using a liner on its own

Sea to Summit says a liner can serve as a standalone summer bag. Air passes through the Reactor's knit easily, so it gives a rough comfort floor of about 60°F (15°C) on its own, or about 50°F (10°C) under a light bag cover. Inside a tent, wind matters less. For a full winter setup, see our cold weather sleeping bag guide.

What to look for when you buy

Questions people ask

Do you need a sleeping bag liner?

Not strictly, but Sea to Summit says a liner keeps oils and grit out of your bag, cuts how often you wash it and adds warmth or wicking.

How much warmth does a sleeping bag liner add?

Sea to Summit estimates up to 4°C / 7°F for its Reactor and up to 8°C / 14°F for its Reactor Fleece, with a suitable bag and pad.

Is a silk sleeping bag liner worth it?

For low weight, yes; Sea to Summit lists its Compact Mummy Silk Blend at 4.6 oz, about half its Reactor.

Can a liner replace a sleeping bag?

Only in warm weather; Sea to Summit puts the Reactor's standalone comfort near 60°F, or about 50°F under a light cover.

Sources

• Which sleeping bag liner should I choose?, Sea to Summit
• Adding warmth with a liner, Sea to Summit
• Choosing and Caring For Liners, Sea to Summit
• Reactor Sleeping Bag Liner, Sea to Summit
• Silk Blend Sleeping Bag Liner, Sea to Summit
• Breeze Sleeping Bag Liner [Insect Shield], Sea to Summit
• Reactor Fleeceweight Sleeping Bag Liner, Sea to Summit
• Comfort Blend Sleeping Bag Liner, Sea to Summit

Sources checked 2026-10-15.