No underwear needed. The Kore is made from a lightweight 4-way stretch fabric and it has a built-in Coolmax anti-odor liner so you can go commando with confidence. The liner was made with comfort in mind so it’s supportive, but not overly compressive. We made the Kore because we wanted a versatile athletic short that performed in a wide range of activities and also looked great outside the gym. The 18.5” outseam falls just above the knee.