Heat Factory Acrylic Sock 12 Pack - Men's Mossy Oak Medium/Large. When exposed to the air an oxidation process takes place that generates heat. Unopened the Heat Factory Warmers have a shelf life of three years or more. Specifications for Heat Factory Acrylic Sock - Men's: Manufacturer: Heat Factory Men's Clothing Size: Medium - Large Gender: Male Sock Height: Crew Color: Mossy Oak Fabric/Material: Acrylic Quantity: 6 packs/2 pairs in each Features of Heat Factory Acrylic Sock - Men's: Men's shoe size 5-8 2 pairs per pack / Case pack = 6 packs Package Contents: Heat Factory Acrylic Sock - Men's Heat Factory M205ML: Acrylic Sock 12 Pack - Men's Mossy Oak Medium/Large