In which denominations is naturism unacceptable? A recent answer on this site made a very broad statement, that "those who live in nudist colonies are not Christians". However, a quick Google search for "Christian naturists" (other search engines are available) shows that there appear to be quite a few people who would disagree with that stance.

Do any denominations specifically stipulate that naturism/nudism is a sin? If so, which?
Bibilically speaking, being "exposed" has always been linked with a shaming - from the time that Adam and Eve realized they were naked and after the fall thus ashamed (Gen 3), to Hosea in which a disgraced and conquered foe was stripped naked, etc...  the general tenor of Scripture is that being naked is an undesirable state.

Since naturism / nudism as a movement is a very new phenomenon (springing in the early 20th century), very few denominations would have felt much need to deal with the issue. There are nudist "churches" (I think of the one at White Tail Resort in VA, for example) but by and large the membership isn't sufficient to warrant the attention of most denominations

All in all, my take on it (and its just my take) is this - being a nudist - i.e. advocating that clothing is unnecessary and socially inhibiting in public - is contrary to scripture mostly because it is an attempt to deny the Fall. In a way, it attempts to deal with the "sin" by stating that it is simply man's invention - a stance that would be at odds with an understanding that God defines what is and is not sin.