SK: Lucky You Trucker Hat100% POLYESTER A sponge trucker mesh cap is likely a variation of the classic trucker hat design with a unique material known as "sponge" incorporated into its construction. Here's a detailed description: Material: Sponge Material: The term "sponge" may refer to a specific type of foam like or soft material used in the construction of the cap. This material adds a unique texture and feel to the hat.