What’s in the can?
Fuel canisters used in single burner butane stoves contain a compressed blend of butane and propane. Butane is the primary component in these fuel canisters, typically accounting for 70 to 80 percent of the fuel mixture while propane makes up the remainder.
How it works
The pressure in the canister keeps most of the mixture in a liquid state although a small amount vaporises into a gas above the liquid. When the canister is attached to a stove and turned on, the gas is forced out of the canister to the stove burner.
In order for this to work, the pressure inside the canister must be greater than the pressure outside.
Cold weather performance
However, as the canister temperature drops below freezing, its internal pressure starts to drop until this is no longer the case and the burner sputters and goes out.
This is because butane stops vaporising at 0.5 degrees Celsius (its boiling point).
Unlike butane, however, propane continues vaporising even in very cold temperatures (down to minus 42 degrees Celsius). This has some interesting implications for cold weather performance.
Propane burns off at a disproportionate rate in temperatures below freezing. As the remaining butane/propane mixture shifts increasingly toward just butane, less and less fuel vaporises until eventually the pressure in the canister drops below what is required to continue feeding the stove. This means that a brand new fuel canister may work for a while in sub-freezing conditions, but can stop working long before the canister is empty.
There’s also another factor that affects a butane canister’s cold weather performance. The process of vaporisation—the changing of physical state from liquid to gas—takes energy. In a butane canister, that energy comes mostly from the latent heat in the fuel mixture itself, which is why a fuel canister will become noticeably cooler while the stove is operating. In cold temperatures, this effect can drive the canister temperature down and stop the burner cold—even if the ambient temperature is above the butane’s boiling point.