Several sites (e.g. englishforums.com) state that there is no difference in meaning between "cross arms" and "fold arms". I was wondering whether this also means that both expressions are used equally frequently, or whether one prevails in everyday language.
Arms that are crossed simply lie across the chest or abdomen in the manner of an Egyptian mummy, while arms that are folded are intertwined, like a pretzel. Likewise if you fold your hands in your lap, your fingers intertwine. Compare that to how one may cross one's ankles, lying one across the other, but you cannot fold your ankles. Nor can you 'fold swords' though obviously you can 'cross swords'. When you sit 'cross-legged on the floor' your shins are parallel, something very different from having one's legs in what's called the 'lotus position', which I supposed could be referred to as 'fold-legged' but obviously isn't. As for the difference in significance of the two stances I would tend to think that crossed arms suggests an imposing or authoritative stance while folded arms are more self-protective; how subjective that reading is I couldn't say.