The only time lipos seem to get warm is in 1/8th buggys where there's limited space and they're are pushed hard due to racing conditioins. Normally in a MT or other surface RC, they don't get much more than warm. If yours are getting hot, they've been undersized electrically - when lipos get hot, that's a sign they're struggling to keep up with the amps demanded by the setup.

Amps supply is more than just C rating, lipo capacity (mah) is also part of it. Usually a 5000mah lipo with 25C or more will usually keep up with the most demanding setups.

Properly sized for teh amp demand, lipos will be dimensionally 'stable'. They def should not puff. Don't get that confused with some lipos that swell slightly on discharge and then return to normal when recharged.