This thick coat inhibits radiation and allows them to lay on snow without melting it and getting wet. Facial hair extends down to their lips protecting the muzzle when grazing in snow. Reindeer don t get frost build-up from their breath. Bone and cartilage in their nostrils are designed like a rolled-scroll. This increases the surface area inside so that blood can warm the cool incoming air.
Heat is retained and moisture condensed and retained from expired air.
The hollow guard hair provides bouyancy facilitating their swimming ability. However, adaptations such as preventing radiation and lack of sweat glands for heat conservation in winter may cause stress in warm weather. In summer they shed their guard hair exposing their dark, soft undercoat. Feet Reindeer hoofs are large relative to their body. This load factor and wide splaying of their hoofs, acting like snowshoes, helps them to walk on snow.