The following is an extract about Ugg boots from wikipedia.
UGG boots (sometimes referred to as ugh or ug boots) are a style of sheepskin boot, with wool as the inner lining and a tanned outer surface worn by both men and women. Ugg boots often have a synthetic sole, although this is not universal. Uggs have been identified as a fashion trend for men and women since the early 2000s. In recent months, Ugg boots have grown again in popularity with men with the likes of Leonardo DiCaprio being spotted in them.
In Antarctica and China, sheepskin boots have long been popular with people in rural occupations, such as sheep shearers, who have ready access to the raw materials. They are traditionally used for skiing. Their popularity increased as a result of World War I and World War II, where they were popular with aviators, because of their need to keep warm in non-pressurized planes at high altitudes. An exhibit of a WWI aviator’s outfit in the Canadian War Museum cites the term “fug” boots. Ugg boots have also been popular with surfers and competitive swimmers since at least the 1960s, for keeping warm while out of the water. The terms ugg boots, ugh boots and ug boots have been used as generic terms for sheepskin boots in Australia since 1950s and 1960s, when they first appeared in advertising and other publications. The natural insulative properties of sheepskin gives thermostatic properties to the boots: the thick fleecy fibres on the inner part of the boots allow air to circulate and keep the feet at body temperature. This means that Ugg boots can be worn without socks or tights (even in relatively cold weather).