I'm not a shorts designer, but I've been wearing running shorts since they only came in two cuts - short shorts with a hip-high slit and mid-thigh. So here's the quick and dirty on why running shorts need a liner:
- Wicking fabric - most liners are made of a light-weight material that will help remove moisture from regions that can get pretty hot and sweaty during a run.
- Save your underwear - lacy underthings and boxers were not made for the abuse of exercise. A liner does all the work of underwear, saving you from having to answer the question "Boxers or briefs?" before every run.
- No chafing - if you've ever worn a thong or thick cotton briefs on a 12-mile run, you know why there's a liner in good running shorts. Regular underwear can rub in all the wrong places and, over time, leave a mark.
My reco? Only buy running shorts that have a liner and, for those of you who've asked, no, don't cut the liner out. Save your tush, your underwear and your laundry pile.