Casual Shirt Pocket Interlining is a kind of layer of cloth that is attached to the inside of a shirt pocket for giving it more durability and structure. The interlining is normally made from a lightweight material like cotton or polyester and is combined to the back of the pocket cloth with the use of heat and pressure. This helps in preventing the pocket from losing or sagging its shape over time, and also helps in preventing items like wallets or phones from poking through the fabric. Further, Casual Shirt Pocket Interlining is mostly found on casual dress shirts and is often invisible from the outside of the shirt.