The Reactor Midweight enhances your sleep system with advanced Thermolite® Pro fabric. Infrared-absorbing ceramic pigments and hollow-core fibers trap body heat, adding up to 6°C-11°F to a sleep system with minimal bulk. Stretch-knit fabric and arm openings allow unrestricted sleep, making it a great fit for any shape sleeping bag. Quick-drying and easy to clean, it features HeiQ Fresh odor control and helps extend your sleeping bag’s lifespan by reducing wash frequency.Sea To Summit Reactor Midweight Liner - Regular Features: Boosts Sleep System Warmth – Thermolite® Pro uses Far Infrared technology and hollow-core fibers to trap and reflect body heat without extra bulk Freedom to Move – Stretch-knit and shaped arm openings allow unrestricted movement, providing natural comfort throughout your sleep Technical Shape and Hood – Ergonomic design with a fitted hood delivers optimal warmth and comfort without extra weight or bulk