Many cyclists do not wear underwear at all, as cycling shorts are tight and padded, and underwear worn underneath the shorts will only bunch up and cause discomfort. People who are not comfortable wearing tight cycling shorts may want to consider purchasing cycling underwear, which can be worn comfortably underneath baggy shorts. Cycling underwear should be adequately padded, comfortable, and lightweight; underwear that is breathable will make the cycling trip even more enjoyable, as the drier the skin stays, the less likely it is to chafe or otherwise become irritated.
Choose cycling underwear that fits snugly. This underwear should fit even more snugly than normal underwear, though it should not be uncomfortably tight. The tighter the underwear, the less chance there will be of excessive movement that can lead to chafing. The waistband should be tight enough to keep the cycling underwear in position at all times, and the legs should feature tight hems that will prevent excess movement. Fewer seams on the underwear means less chance of chafing, though some underwear with several panels will have more seams; this is done to promote a tighter fit. Make sure the seams are not excessively large or rough to prevent irritation.
The most important part of any cycling underwear is the padding. The padding should be thick enough that it provides support while sitting on the bike saddle, but not so thick and large that it interferes with normal leg movement. If the padding is too thick upon purchase, don't worry too much, as the padding will often compact after several uses. Some padding is made to be antibacterial; these underwear options will be more expensive, but it is well worth the investment as the padding will prevent bacteria build-up that can be potentially harmful.
The cycling underwear should be exceptionally breathable. Synthetic fabrics are often used because they are specifically designed to wick moisture away from the skin, keeping it dry and comfortable. Moisture building up on the skin can lead to chafing and hot spots, which will only worsen over the course of a bicycle ride. Synthetic materials will keep the skin dry and comfortable, but remember that synthetic materials tend to capture a significant amount of body odor, which means the underwear may smell quite bad by the end of a ride. Wash the underwear frequently, and choose materials that will withstand frequent washing in a washing machine.