The Seirus Heatwave Sock Liner uses Seirus’ dual-stage heating system to maximize the amount of warmth a liner can generate. The reflective poly-nylon lining helps you retain up to 20% more body heat while kinetic energy from the wicking process is harnessed to provide an additional 4-5 degree increase in warmth. You’ll relish your Seirus Heatwave Sock Liners almost as much as you relish kicking back in front of your wood stove.