Sleeping Bags Aren't Enough
The ground below your tent usually is hard, cold, wet and bumpy. A sleep pad will not only make you more comfortable, but it will also help keep you dry (even in a leaky tent) and prevent your body heat from escaping into the the ground.
Sleep Pad vs. Air Mattress
Air mattresses are larger, thicker and bulkier than sleep pads and require an electric or manual pump to inflate. Sleep pads are thinner (about 1 1/2 inches thick), narrower (normally just wide enough for one person) and easier to store and carry.
Inflatable Sleep Pads
Inflatable sleep pads are composed of a foam core, a nylon shell and an air valve. When the valve is opened, the mattress inflates as air fills the foam cells. Deflation is easy: Just open the valve and slowly roll up the pad so the air escapes.
Foam pads are significantly less expensive than inflatable pads, and because they don't inflate or deflate, you don't have to worry about punctures or valves malfunctioning. The downside: They aren't always as comfortable as inflatable pads and tend to be bulkier and harder to store.
Pay attention to the length and width of a camping sleep pad. A too-small pad means that your limbs might be resting on a cold tent floor. If low temperatures are a consideration, ask about the pad's "R-value," which reflects how well the pad prevents loss of body heat. The higher the R-value, the better the pad's heat retention.