Question : What is a Aluminium Composite Sign? Aluminium composite signs are a rigid, durable aluminium composite material consisting of two thin sheets of aluminium bonded to a solid polyethylene plastic core. This is a unique composition that makes it approximately half the weight of raw aluminium. Aluminium composite signs are the flattest panel on the market, offer a superior surface for direct digital printing as well as mounting graphics. Aluminium composite signs provide excellent durability in outdoor applications and won't bow or warp.