Bouldering pads are used as a safety mats in outdoor bouldering. In sport climbing, a thin pad is sometimes used to secure the first moves of the leader. Bouldering pads are usually about 10 cm thick, weigh 5-10 kg, are collapsible and can be carried on the back. A sit-start pad is a smaller, thinner pad that fits between the larger pads for carrying and is a good way to secure your butt when trying that tricky low sit-start.