Icebreaker made the Siren Hipkini out of ultralight merino wool with a touch of Lycra for a great fit. Soft and gentle against your skin, the Siren has a low rise and full coverage in the back. The merino naturally deals with odor so you can get through multi-day backpacking treks and hut-to-hut ski tours without using up precious packing space with extra undies.