Things to consider when buying a sleeping bag are it's shape, warmth rating and, if backpacking, it's weight and pack size. Shape wise sleeping bags are normally square or feature a 'mummy' shape. Square bags provide plenty of wriggle room and are preferred by many as they do not feel as constrictive as a mummy style bag. Due to the extra fabric and insulation square bags do not pack as small but this would only be an issue for backpackers looking for the smallest pack size possible. 'Mummy' shaped sleeping bags taper with the body providing a tighter fit, reducing the area that your body would need to heat and will in turn provide more efficient insulation.
Warmth ratings are measured by season rating with 1 Season being the least insulating and 4 Season and above the most and more appropriate for cold climate camping. There are also two types of insulation used with synthetic insulation more common and much cheaper to produce while down is used in higher end, technical sleeping bags to insulate against extreme cold temperatures. By using a sleeping bag liner thermal efficiency can be greatly increased and also serves to keep the bag cleaner.
A sleeping mat is a pretty vital bit of kit as it will insulate you from the cold ground as well as providing a comfortable surface on which to lie on. Roll mats are the most basic form of sleeping mat, generally made from foam which makes them very reliable although they are not that compact when rolled up. Self inflating mats are far more compact and are self inflating to a point but do require topping up via valves. These mats are more expensive than roll mats but utilise expanding foam and/or cells that insulate and provide good levels of comfort.
For ultimate comfort when camping air beds provide a mattress like sleeping experience for relatively little cost. It's always recommended to use a air pump with these beds though as it takes a lot of air to fill them.
Camp beds are frame based beds that raise you up and off the floor.
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