Having some trial and error experience with Jetboil, I can point out a few things about the fuel, and a few things that have worked for me. First, NOT all canister fuel is created equal. Here are a few for comparison, each with the relative temp values of each fuel – canister fuels are generally a mixture, and they are different ratios.
This is important since all fuels vaporize at different temps. Without some fuel left in the canister that is vaporized – it will leave no pressure to feed fuel to the stove. n-Butane vaporizes at 31°F. Isobutane vaporizes at 11°F. Propane vaporizes at -43°F. Essentially what that means is that n-Butane will not vaporize below 31°F, while the other mixtures do and leave useless liquid n-butane in the canister. At 11°F the same phenomenon happens with Isobutane.
So.. A low (or no) n-Butane mixture, and higher propane mixture are more suitable for colder temps.
There are a few work arounds to this problem;
1. use a higher propane mixture (SnowPeak silver can) in colder temps.
2. Keep the canister warm against your body heat in your jacket or sleeping bag. Also warm water or, yes, urinate on it (heard of that, never tried it).
3. I know some extreme alpinist (likely a few here) use a candle flame to gently heat canisters – but unless you are savvy doing this, I would not attempt it – the result of exceeding 50C can mean a bomb on your hands (or.. hand).
4. Another method I have seen is to use a heat exchanger, basically a piece of copper wire that wraps from the flame around the gas cylinder which draws heat to the cylinder (again see #3 above, if not savvy – best not to attempt).
5. A method I have used that has worked well into the -10 – 15F range is to use an old drink cozy or similar foam and keep the gas cylinder in it (insulation). In extreme cold temps or windchill, a chemical hand warmer at the base of the cozy works awesome. It is just enough heat to provide optimum warmth to efficiently keep the gas vaporized, but they do not generate enough heat to endanger the cylinder.
In the winter I use the SnowPeak fuel, and in the summer I use JetPower (Jetboil) or MSR – whichever I find cheaper, because essentially they are the same fuel mixture. Again, the SnowPeak fuel contains the highest propane mixture, so note this fuel will burn [much] faster. If you are in milder temps you will get more mileage from the MSR or Jetboil fuels.
The principles of inverted canister stoves; allow the heavier gases to settle near the valve and the propane toward the top which forces the other gases out prior to propane so you are not left with zero vaporized gases – hence no pressure.
A final word: whichever method you use, keep in mind the fuel canisters have a concave bottom for a reason. If the pressurized gas over-expands (overheats), this concave design theoretically allows the canister to ‘pop’ out prior to exploding. Personally I am not brave enough to use a candle to preheat the fuel, but the #5 cozy idea combined with the SnowPeak fuel I listed above has worked for me quite well.
Lastly that piezo ignition everyone complains about (to include me). Piezo ignition is a PZT crystal – it will begin to fail above 10,000 feet, and will not work at all above 13,000. The reason is simple physics. Always have a Bic flint lighter or Arc matches handy.. I could never figure out why my piezo would not work at altitude. It was briefly addressed at BRC last week, and answered my lifelong question. So don’t worry, it’s not just you – they are unsuitable for mountaineering.
Wiki on retarded piezo ignition: http://en.wikipedia.org/wiki/Piezo_ignition