The sunshield has five layers to mitigate the conduction of heat.[1] These layers are made of the polyimide film Kapton E, which is stable from −269 to 400 °C (−450 to 750 °F).[3][6] However the thin films are delicate - accidental tears during testing in 2018 were among the factors delaying the JWST project,[15] and Kapton is known to degrade after long term exposure to Earth conditions.[16] The sun-facing layer is .05 mm (0.002 in) thick, and the other layers are .025 mm (0.001 in) thick.[3] All layers are coated on both sides with 100 nm of aluminum, and the Sun-facing sides of the outermost two layers are also coated with 50 nm of silicon "doped" with other elements.[6][3] This helps the material survive in space, radiate excess heat, and to conduct electricity, so a static charge does not build up on the layers.[6]