What's the difference between propane, butane and isobutane? What stove fuel should I use?
All three gases are canister fuels. Stored under pressure, the fuel vapors compress into liquid, making it possible to pack a lot of fuel into a small canister. When the liquid fuel is released from the canister, it re-vaporizes and burns hot. Canister fuels burn cleanly, don't require priming, deliver almost instant heat and require only simple burner stoves that can weigh just a few ounces.
Under pressure, propane becomes liquid-propane gas (LPG), commonly used to heat homes and fire up Dad's barbecue grill. Propane burns the hottest and best in below-freezing temperatures and is the best of the three gases. But because LPG has to be stored under much higher pressure than the other fuels, it requires a heavy steel canister, making it impractical for climbing stoves. Propane canisters also have large screw tops that won't fit onto lightweight climbing or backpacking stoves, so rule it out as an option. Propane is the ideal canister fuel for car-camping stoves such as the ubiquitous two-burner Coleman.
Butane is the gas you find in Bic lighters. Because it operates at a much lower psi than propane, it can be packaged in lightweight canisters. Butane works well in above-freezing temperatures where canister pressure is sufficient to deliver gas to the burner, but as the thermometer plummets so does canister pressure, which was low to begin with. In winter, or on a cold mountain, the barely trickling butane doesn't cut the mustard. To help propel butane out of the canister, it is usually mixed with 20 to 30 percent propane. Propane improves performance, but because the gases burn off at different rates, you run out of propane first, leaving you with the nearly unusable butane.
Isobutane is another low-pressure fuel and has better cold-weather performance than butane, but barely. It, too, is often mixed with propane for cold-weather use.
For cooking in temps above 40, the type of gas you use doesn't matter -- get whatever is handy and cheap. In colder temps you'll need a blended fuel. I've found that the propane, isobutane and butane mixes work best, although you still must keep the fuel warm for optimal performance. The easiest way to do this is to use two canisters, one on the stove and the other in your jacket or bag. When the stove canister cools and loses pressure, swap it out with the warmed canister. A sloppy option is to set the canister in a shallow pan of water, which will warm the canister. I've also tried keeping canisters warm with chemical heat packs, with poor results. Homemade heat-exchangers, such as flattened copper tubing coiled around the canister and with one end protruding in the flame, certainly warm the fuel. So much so, in fact, that use of such a contraption may soon have you counting your 70 virgins in paradise. A recent promising invention is the inverted canister stove, the Coleman Fyrestorm. This unique design flips the canister upside down, using gravity to feed the liquid gas from the canister, rather than relying on canister pressure to deliver gas vapor to the burner. Because canister pressure is irrelevant, cold-weather performance could rival that of white gas, and burner output should remain constant even as the canister empties. In the coming months I'll be testing the Fyrestorm, comparing it to conventional canister and white-gas stoves. (The Fyrestorm also burns white gas; it could be the most versatile stove yet.) Jetboil also has an inverted canister stove in the works. Coupled with the Jetboil heat-exchanger system, that stove could be the ticket. I'll test that stove as soon as it is available and let you know if it's the schnitzel.