Thickest tree bark

The species of tree that produces the thickest bark of all trees is the giant sequoia (Sequoiadendron giganteum), which grow indigenously in the Sierra Nevada Mountains of California, USA. Mature trees almost always have bark 25-35 cm (9.8 in-1 ft 1.8 in) thick, and a thickness of 50 cm (1 ft 7.7 in) is not uncommon in many groves. The bark of giant sequoia is one of the most insulating structures in nature. The bark fibres are organized in a series of cross-fibre bundles, creating a 3D "net" filled with airspaces, much like attic insulation. When a tree or branch falls against it (or if one pushes in with their hand), the bark compresses, but can later rebound to its original shape because the fibre-bundle network diffuses the impact and then relaxes. During fires, this air-filled bark can keep the cambium of the tree from overheating. The maximum recorded depth is 78.7 cm (2 ft 7 in), from Redwood Mountain Grove in Kings Canyon National Park.

The bark protects the tree from disease and insect damage, but one of its main functions, particularly as the sap is water-based (as opposed to resin-based) is to defend the tree from fire.