In camping, a sleeping pad, sleeping mat or ground pad is a simple device often used in conjunction with a sleeping bag. Its purpose is to provide padding and thermal insulation. The ground may become quite cold at night, and is often covered with sticks, small rocks, and other objects that may make sleep difficult. A sleeping bag does not provide adequate protection against either hazard, but a sleeping pad does.
The simplest sleeping pads are sheets of foam rubber, closed cell foam or a reflective metallized plastic material, rolled up or folded for storage. The latter provides little extra comfort, but gives good insulation. It is popular because of its low mass and volume. More expensive, and heavier, inflatable models are designed with interconnected air cells that may be compressed for maximum compactness, or inflated through a valve for maximum padding.
Self-inflating air mattresses are available for backpackers, e.g., Insulmat & Therm-a-Rest®. As a partial misnomer, these pads will only inflate to the ambient air pressure, and usually will need a couple of breaths of air into the chamber to firm up the sleeping surface. There are two types of self inflating air mattresses; edge bonded and fully bonded. Edge bonded sleeping pads have the fabric bonded to the self inflating foam on the edges,as the name implies, and are cheaper to build then fully bonded mattresses. If there is too much air added to the chamber, these pads will "pillow" up in the center, and is why it is best not to blow air into them. Fully bonded pads have the fabric bonded to the foam on all sides. These offer superior comfort and a smaller packed volume than traditional foam sheets, however these are more prone to puncture.
In the 90's other manufacturers have offered new designs. Exped uses goose down to fill air inflated chambers in contrast to foam. This does not self-inflate so they have built an air pump into the stuffsack so that moisture from a person's breath does not saturate the down and eliminate all of the loft. To update this approach, 2004, Pacific Outdoor Equipment pioneered the Air Loft tube sleeping pads, e.g. the Max Thermo. Air Loft sleeping pads were designed to reduce the pack weight and size of the sleeping pad, and keep the camper a lofty 2.5 inches above the ground. Big Agnes and Ajungilak have copied this approach that implores draping a polyester fibre fill insulation to help reduce air circulation. Perhaps the ultimate in lightweight solutions, yet least durable and most likely to only last one night is the Balloon Bed.
There have been other hybrid designs created that have complimented the lightweight craze that is sweeping the backpacking community. Pacific Outdoor Equipment has created a sleeping pad that melds self inflating pads with closed cell foam pads. Their Hyper-Lite series of sleeping pads offer a self inflating foam and closed cell foam under the sleepers shoulders as well as hips to increase the necessary cushion. This eliminates cold spots for the sleeper. Under the legs, this pad uses close cell foam to sustain insulation, and offer a little padding.
Recently, there have been leaps and bounds made along the sleeping pad front. With lighter weight materials and new designs, these pads have a focus of innovation by many experienced designers. Pacific Outdoor Equipment has fused the Self Inflating sleeping pad with an Air Loft pad. With berms on the edge of the pad that start from the shoulders and trace the edge to the foot of the pad, it sleeps wider, is lighter, and compacts as small as a Air Core pad, e.g. the size of a coffee can. Gender specific pads have been designed for the growing number of women who are spending more time in the backcountry as well as the weekend car camping trips. These pads are designed after studies down by several universities, and because of the need for a higher performance sleeping pad. Providing more support in the hip area as well as extra insulation in the foot box, these new Women's Specific pads offer much needed comfort in the trail. Furthermore, with advances in technology that allow the weaving of bamboo fibers into fabrics and the continuing green movement to take steps towards a more healthy planet, outdoor companies are manufacturing pads that last longer and are made from greener materials.
In the UK, pads are sometimes known by the slang term splat mat. The foam sheet variety has been known for years by the brand name 'Karrimat'.