'Soft' cased lipos are not really that soft at least as far as the ones I'm using - Turnigys, Neuenergys, Hyperions and Flightpower lipos - 2S, 3S and 4S lipos - these have never shown even a hint of a strap impression.

Soft is somewhat of a misnomer, at least as far as the ones I've used. Yes, they don't have a truly hard outer skin, like plastic or composition, but 'soft' may be a poor description at least with the lipos I have used.