Tent fabric may be made of many materials including cotton (canvas), nylon, felt and polyester. Cotton absorbs water, so it can become very heavy when wet, but the associated swelling tends to block any minute holes so that wet cotton is more waterproof than dry cotton. Cotton tents were often treated with paraffin to enhance water resistance. Nylon and polyester are much lighter than cotton and do not absorb much water; with suitable coatings they can be very waterproof, but they tend to deteriorate over time due to a slow chemical breakdown caused by ultraviolet light. The most common treatments to make fabric waterproof are silicone impregnation or polyurethane coating. Since stitching makes tiny holes in a fabric, it is important that any seams are sealed or taped to block these holes and maintain waterproofness.
Rain resistance is measured as a hydrostatic head in millimetres (mm). This indicates the pressure of water needed to penetrate a fabric. Heavy or wind-driven rain has a higher pressure than light rain. Standing on a groundsheet increases the pressure on any water underneath. Fabric with a hydrostatic head rating of 1000 mm or less is best regarded as shower resistant, with 1500 mm being usually suitable for summer camping. Tents for year-round use generally have at least 2000 mm; expedition tents intended for extreme conditions are often rated at 3000 mm. Where quoted, groundsheets may be rated for 5000 mm or more.
Many tent manufacturers indicate capacity by such phrases as “3 berth” or “2 person”. These numbers indicate how many people the manufacturer thinks can be fit snugly into a tent with just sleeping bags. These numbers do not allow for any personal belongings, such as luggage, inflatable mattresses, camp beds, cots, etc., nor do they allow for people who are of above average height. Checking the quoted sizes of sleeping areas reveals that several manufacturers consider that a width of 150 cm (5 feet) is enough for three people — snug is the operative word. Experience indicates that camping may be more comfortable if the actual number of occupants is one or even two less than the manufacturer’s suggestion.
If the tent will be used where mosquitoes, gnats and other biting insects are expected, it should have all window, vent and door openings covered with fine-mesh “no-see-um” netting.
Tents can be improvised using waterproof fabric, string, and sticks. This allows them to be easily built and moved.
