A one-piece, lightweight, molded plastic hat that comprises, in combination, a thin, molded plastic sheet forming a hat wall dome having an inner side, the sheet at the dome everywhere having thickness less than 3/16 inch; the sheet at the dome forming a corrugation having a local portion defining...http://www.google.com/patents/US5713083?utm_source=gb-gplus-sharePatent US5713083 - Thin-walled plastic hat structure
