I was wrong...it's r600a that is isobutane...it's a replacement for r12 and r134 and favored because of it's low global warming potential according to some website after 2 minutes of googling. Sounds correct to me though. Edit. I just read that it is the preferred choice for domestic refrigerators worldwide...It's used by most major OEM (Original Equipment Manufacturers) in domestic refrigeration applications. Am I the only one worried about having a relatively large amount of isobutane in my kitchen? I know if it leaks enough it would only take one spark from something in most kitchens...light switches, relays, or the pilot light if you have a gas stove...heck alot of older homes I've worked on in Richmond had gas water heaters in the kitchen itself or in a pantry...