Men and women wore "long johns" inside outer clothing. Women referred to them as "under muslins." As long as the cotton fabric stayed relatively dry, it helped preserve body heat. Both wool and silk underwear provided better insulation than cotton, but wool was too scratchy for most individuals and silk was too expensive. It would be many years before synthetic fibers would combine the best properties of the natural fibers. In the mountains men wore wool shirts and pants. Cotton shirts were worn during very hot weather, but only the more stylish of male Mountaineers carried cotton pants as a change of clothing.

During the 19th and early 20th century women were expected to wear dresses, regardless of whether they were in the parlor or on the mountaintop. In 1890 Fay Fuller, the first woman to climb Mount Rainier, was considered daring but practical because she wore bloomers instead of petticoats under her shortened ankle-length skirt. Until the latter part of the nineteen twenties the dress code for women remained strict. Female climbers wore dresses or blouses and skirts while travelling to and from the backcountry. They changed into wool knickers or English Gabardine trousers when they reached wilderness areas. Both men and women who sat down on snow slopes in order to slide or glissade wore heavy khaki trousers with a reinforced and paraffined seat, called "tin pants."