Warming pack pockets are lined with DuPont Tyvek®, a lightweight microporous non-woven material for HEATPAX® regular size warming packs|Short elastic strip in the forehead area keeps the liner snug to face|Some styles available with strip of reflective film above back of neck|Flame Retardant (FR) treated until washed styles also available|Shoulder, mid, regular lengths and 2-layer or 3-layer styles available