This range utilises the Pertex® and Pile system and is intended for winter use for various specified activities. Depending upon the usage, two types of Pertex are used as stated: Pertex 5 which is windproof to 35-40mph (56-64kph) and resists rainfall to the rate of 1/2 inch per hour (12.7mm per hour). Pertex 6 is windproof to 45-50mph (72-80kph) and resists rainfall to the same rate of 1/2 inch per hour (12.7 mm per hour). Apart from windproof performance, Pertex 6 is more abrasion resistant and is therefore used in clothing for activities where resistance to abrasion is a major concern, such as climbing. All Pertex fabrics are highly breathable, independent tests prove Pertex to be more highly breathable than any other similar fabric available. None of the Buffalo products are intended to be waterproof, they are proofed to repel water as stated above, but they will all keep the wearer warm even when the garment is wet, as long as the wearer keeps active or if stationary just exercise every 10 minutes to keep their body temperature from dropping. All the lined overhead garments work most efficiently when worn next to the skin. In this way the pile fabric wicks moisture away from the skin more rapidly, where it is then dispersed by the Pertex to the external surface to evaporate and keep the body dry and free from chilling. This is the fundamental principal of the Pertex / Pile system: to keep moisture away from the skin, because in cold conditions if perspiration is not allowed to escape it is retained and rapidly cools causing chilling. Although the Mountain Shirt and other Pertex / Pile overhead garments are intended as a base layer to replace various other layers of clothing, it is recognised that in certain circumstances an under layer is sometimes needed, but if this is the case then that layer must be of a material that is able to disperse moisture away from the skin, it is extremely dangerous to wear an under layer of cotton as cotton retains moisture and very rapidly chills the body in even moderately cool temperatures, causing hypothermia. In terms of all Buffalo overhead garments intended to be worn next to the skin, the side zips are an essential feature, not only allowing access, but to adjust for ventilation, enabling the user to regulate their body temperature. Active usage may require the zips to be lowered to ventilate and keep the body cool, but once at rest the zips should be closed to retain the body heat and keep the wearer warm whilst inactive. The DP System is so effective at transmitting moisture that the best way of drying it is to wear it.