Bioprene

Bioprene (noun): (a) An abundant layer of hypodermis or subcutaneous tissue, that is mainly used for fat storage and which comes with age or inactivity. (b) A purposefully added layer of fat used as a natural means to help tolerate cold water by channel swimmers.

Origin: bio + neoprene or polychloroprene, a synthetic rubber that is used for wetsuits. Neoprene is the DuPont trade name for its brand of polychloroprene.

I am not getting fat, I am just wearing bioprene.

The marathon swimmer ate a box of donuts every morning in order to add to his layer of bioprene.