Kap-Bak is designed to fit most adjustable caps, but not every adjustable cap on the market. Cap manufacturers vary widely in how they build the back of a hat, and two factors in particular affect fit: head size — both larger and smaller than average — and the size and shape of the back opening itself.

Our current design is built for the standard back opening, which measures approximately 3 inches across the bottom (at the strap) by 2.5 inches in height. Caps with openings meaningfully larger or smaller than this may not seat correctly.

If your cap’s opening is narrower than 3 inches, the Kap-Bak can be adjusted: the polyester fabric can be trimmed to a smaller width and the cut edge sealed to prevent fraying. We are happy to walk you through this — please reach out before you cut.

We are currently developing additional sizes to accommodate a wider range of head sizes and back openings. Those are not yet available, but we will announce them here and on our social channels as soon as they are.

Questions about fit? Contact us and we will help you determine whether Kap-Bak works with your cap.