June 24, 2026 | Sleeping Bags • R-Value Guide • Ultralight Gear
A sleeping bag liner adds warmth by trapping a still-air layer between your body and the liner fabric. The temperature boost depends on the fabric's CLO value per ounce: silk produces roughly CLO 0.5 for a 5 oz liner (+5°F boost), fleece produces CLO 1.2 for an 8 oz liner (+15°F), and Thermolite (a hollow-core polyester fiber that traps air inside each fiber strand—not just between fibers) produces CLO 1.8 for a 6 oz liner (+15-25°F). A liner adds zero warmth if it is compressed—it must fit loosely inside the sleeping bag to create the still-air gap. Here is the comparison.
| Liner | Material | Weight | Temp Boost | Packed Size | Price |
|---|---|---|---|---|---|
| Sea to Summit Thermolite Reactor Extreme | Thermolite Pro (hollow-core polyester—each fiber is a tube with air trapped inside. Standard polyester is solid—Thermolite's hollow core increases surface-area-to-volume ratio, trapping more still air per gram.) | 8.7 oz | +25°F (Sea to Summit claims this—independent backpacker testing suggests +15-20°F more realistic. Manufacturer claims are laboratory-measured with no drafts, no pad loss, no movement. Real-world subtract ~5-8°F from lab claim.) | Softball (compresses into included stuff sack) | $65 |
| Sea to Summit Silk Travel Liner | 100% mulberry silk (16 momme weight—momme is the silk density unit used in the textile industry. 16 momme = 68 g/m². Higher momme = denser weave = more durable but heavier. 16 momme is the sweet spot for durability vs weight in a sleeping bag liner.) | 5 oz | +5-7°F (silk traps air between the fibers with minimal weight. The warmth-to-weight ratio is high—5 oz adds 5°F, roughly 1°F per ounce. But the absolute warmth added is low—5°F won't save a 30°F bag on a 20°F night.) | Tangerine | $65 |
| Cocoon Merino Wool Mummy Liner | Merino wool (150 g/m²) — absorbs moisture without feeling wet. Wool's natural antimicrobial property (lanolin + fiber structure) reduces odor over multi-day use—a silk or synthetic liner worn for 7 consecutive nights develops more odor. | 10 oz | +10-12°F | Grapefruit | $75 |
A down sleeping bag should be washed as infrequently as possible—each wash cycle removes natural oils from the down clusters, reducing loft and warmth. Drying a down bag takes 3-4 hours in a commercial dryer with tennis balls (to break up clumps). A liner is machine-washable in 30 minutes and protects the sleeping bag from body oils, sweat, and sunscreen residue. For the $65 cost of a silk liner vs the cumulative loft-loss from washing a $400 down bag every 15 nights, the liner pays for itself in the first year. See our sleeping bag guide and down vs synthetic comparison. View Thermolite → View Silk →
Disclosure: BestCampGear is a participant in the Amazon Services LLC Associates Program. CLO values from textile physics literature. Momme silk weight from textile industry standards. Thermolite hollow-core fiber from manufacturer technical documentation.