Breathable but Warm Sleeping Bag Liner.

The Sea to Summit Reactor Sleeping Bag Liner enhances your sleep system by adding up to 14°F (8°C) of warmth, making it an excellent cold-weather option for those needing additional insulation. Constructed with hollow-core Thermolite® fibers, it traps heat efficiently while remaining breathable and lightweight. The stretch-knit fabric offers exceptional comfort and freedom of movement. Its mummy shape with a drawstring hood minimizes heat loss, and the liner packs down smaller and lighter than fleece alternatives. Easy to care for, it's machine washable and comes with an Ultra-Sil™ stuff sack for compact storage.