Disclosed is a release liner having a multilayer structure of at least three layers including two surface layers and an intermediate layer, in which one of the two surface layers contains a high-density polyethylene, the other contains a low-density polyethylene, and the intermediate layer contains a low-density polyethylene alone as its resin component. The four-point link includes four link arms which are fixed to one another by a central region and which extend away from the central region to form a cross. A drain hole is provided to establish communication between the inside and outside of the insulator.