Sea to Summit Reactor Lightweight Liner

The Sea to Summit Reactor Lightweight Liner isn't a standalone sleeping bag but an insert that extends the usable range of an existing sleep system. Thermolite Pro fabric, made from 100% recycled polyester, adds up to 4°C of warmth for just 255g (Regular size) — a practical way to stretch a bag's temperature range without buying a warmer one. The mummy shape follows a typical sleeping bag's contours, and an internal length of 193cm suits users up to 185cm tall. The liner has no water-resistant treatment, which makes sense for an inner-layer fabric — it functions as both a thermal and hygienic layer between body and bag. A stuff sack is included, and the 18 × 10cm packed size takes up minimal room in a pack. Its use falls into two categories: as a nighttime booster inside a three-season bag on colder nights, or as a standalone lightweight sheet in hot summer conditions where a full sleeping bag would be overkill. The unisex cut makes the Reactor a versatile add-on for any sleep setup.