Hi Elizabeth. Sometimes they replace a slip, but other times I still prefer to wear a slip and the slip shorts. If they are silky enough to keep your skirt from hiking up as you walk and the skirt is not sheer, I just wear the slip shorts. But if the dress is sheer and needs a slip I still wear one. And if the dress is course – such as some linen – and the slip shorts are not especially silky, my experience is that the skirt will still crawl up as you walk so you need a slip. I really wear the slip shorts mainly to prevent thighs touching, which is just a pet peeve of mine. I don’t really get thigh chafing, but I just can’t stand for my thighs to touch at all. Yeah, I’m weird like that..,