Optimized for minimal weight and maximum warmth, the Reactor Lightweight enhances sleep system performance with advanced Thermolite® Pro fabric, which uses infrared-absorbing ceramic pigments and hollow-core fibers to trap body heat. Adding up to 4°C|7°F of warmth with minimal bulk, it’s ideal for ultralight expeditions. Stretch-knit fabric and articulated arm openings ensure unrestricted mobility. Treated with HeiQ Fresh odor control, it’s quick-drying, machine washable, and helps prolong your sleeping bag’s lifespan by reducing wash frequency.