How do sleeping bag liners add warmth?

Liners add a layer of trapped air between your body and the sleeping bag. Silk liners add roughly 3°C, fleece liners 5°C, and thermal (Thermolite) liners up to 8°C. They also keep your bag cleaner, which maintains loft and insulation performance over time.

Does the sleeping pad really affect warmth?

Yes, significantly. The compressed insulation under your body in a sleeping bag provides almost no warmth — your pad is responsible for ground insulation. Each R-value unit adds roughly 2°C of comfort. An R5 pad can make a summer bag usable in much colder conditions.

How does altitude affect my sleep system?

Temperature drops approximately 1°C for every 150m of altitude. A campsite at 900m on a Scottish hill can be 6°C colder than the valley floor. Wind exposure at altitude further reduces effective temperature. Always plan for the coldest realistic conditions.

Should cold sleepers buy a warmer bag?

Yes. If you consistently feel cold at night, subtract 5°C from your bag comfort rating when planning. Women, smaller people, and those who sleep cold should choose bags rated 5-8°C below their expected minimum temperature. A warm liner is a lighter alternative to a heavier bag.

CampCalcs

Sleep System Insulation Combiner

Combine sleeping bag, pad and liner ratings to find your total system comfort temperature.

Sleeping Bag Comfort Rating

EN/ISO comfort rating

Sleeping Pad R-Value

Sleeping gear specification

Liner TypeBeer or gas line parameter

Campsite Altitude

Pressure in pounds per square inch

Wind ExposureEnter the wind exposure

Sleeper TypeEnter the sleeper type

How We Calculate This

Effective Comfort Temperature

Effective temp = Bag comfort rating - Liner boost - Pad boost + Altitude adj + Wind adj + Sleeper adj

Liner Boosts

Silk: +3°C, Fleece: +5°C, Thermal: +8°C

Pad Contribution

Each R-value unit adds approximately 2°C of comfort.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Always verify conditions and use proper safety equipment outdoors.