A Deckle is a belt used along with a mold to gather up woodpulp from a vat for pressing and drying into sheets. It helps to control the size of the paper produced. Paper with a feathered or soft edge is often said to have a "deckled" edge for this reason (as opposed to a cut edge).

Paper can have two types of deckled edge: natural deckles or tear deckles. Natural deckles are the result of the deckle used in mould-made paper, whereas tear deckles are the result of tearing the paper. Often mould-made paper will have a combination of deckled and cut edges depending on the specific size of paper required.

In film processing, deckles are die inserts that set the coating width of a slot die coater or the extrusion width of an extrusion die. They work by constraining the flow as the material exits the die. Since some materials have a tendency to neck in or spread out after leaving the die, deckle position may need to be compensated to achieve the target width.