A dry bag is a type of bag which seals in a watertight manner. Dry bags are often used in kayaking, canoeing, rafting, and other outdoor activities where sensitive items would otherwise get wet as well as extreme sports such as skiing and snowboarding. They are often a construction of plastic film, plastic-coated fabric or waterproofed fabric which is formed to create an impermeable, water-ingress protected bag. When using a dry bag, it is vital to ensure the roll top closure is folded at least three times, to create a watertight seal. Construction techniques include welding, sewing (where a seam-tape is used to seal over any needle-holes) and gluing.