Sleeping bag basics

Synthetic or down?

The main decision to make is whether to get a synthetic or down bag. Our table below explains their pros and cons. For kids or casual use like weekends away in a bach or crib, a synthetic bag may be all that's needed.

Down sleeping bags are the way to go, particularly if space is an issue. But they're much more expensive - a high-quality down sleeping bag will set you back $400 to $900, whereas a synthetic bag will be more in the range of $100 to $500.

They're also trickier to take care of (see "Caring for your sleeping bag").

Shape

There are two main shapes. Semi-rectangular bags have zips on one side and at the bottom - handy in summer, when you're too hot to be enclosed.

Tapered bags (or mummy bags, as they're sometimes called) don't usually fully unzip and become narrower nearer the feet.

Chris Tews from the Mountain Safety Council says this design is more efficient. He recommends looking for "an insulating flap over the zip" and says a hood "will also add considerably to the warmth".

Temperature ratings

Most sleeping bags come with a temperature rating. But how can you work out which warmth rating will suit you? Unfortunately, temperature ratings are an inexact science and vary from brand to brand. And while a sleeping bag might claim to be "usable" down to -25°C, that doesn't mean you won't be uncomfortably cold at that temperature.

Figure out the likely temperatures you'll be facing on your trip based on location, weather reports and the heights you'll be going to. Then look at sleeping bags that claim to match these and err well on the warm side. If it gets too hot, you can unzip the bag or remove layers.

It may be tempting to save by buying a sleeping bag with a broader warmth rating. Don't give in to this - a sleeping bag should be treated as an investment. You can't change your mind when you're on top of a mountain trying desperately to stay warm.