MSR IsoPro is an 80/20 blend of isobutane and propane, with the purest isobutane (5% or less n-butane) of any canister fuel.__ This clean-burning formulation maintains higher internal pressure at lower temperatures than standard butane/propane mixtures, giving you superior cold weather performance and more consistent output over the life of the canister.__ This 4 oz. canister is sized to fit inside the MSR 1.0L Reactor Stove System.Clean-Burning: Zero-maintenance combustionFuel Gauge: Built-in float gauge determines how much fuel is leftRecyclable (consult your local recycling center for regulations)