I have read - with great interest - the information on this page. It is all terribly informative. Here in Britain, we are currently researching the phenomenon of chafing. I have found that there is no quick cure to the problem, other than total removal of underwear. A bold step, yes, but necessary. Contact between buns and fabric only tends to become troublesome when layering is involved, i.e. when more than one garment is involved around the butt area.
However, a recent census has suggested that (here in Scotland at least) the population is reluctant to shed underwear due to climactic conditions. We live in a country where "mistybutt" is commonplace, for example. If, then, panties or boxer shorts etc MUST be worn, I would suggest the following:
Dr Andrew McMillan