Longjohns

Longjohns are a type of underwear that cover most of the body. It is usually worn by humans around winter to help them keep warm in cold temperatures.

In the EMPATH: The Luckiest Smurf story series, Smurfs also tend to wear longjohns in really cold temperatures, although Empath's bodysuit from Psychelia achieves the same purpose while managing to be lightweight.