Alternatively, just trace the base of the old seat onto your new piece of plywood (especially if it’s not a perfect circle, square, or rectangle).
If you’d rather not cut the plywood yourself, most hardware and home improvement stores can cut it for you. If you’re restoring an old seat and the wood is still in good condition (no cracks or mold), feel free to reuse it for the new seat.
3 in (7. 6 cm) thick foam provides a nice, comfy cushion. If you want your cushion thinner, opt for a 1 inch (2. 5 cm) or 2 in (5. 1 cm) foam.
The batting layer reduces the friction between the foam and seat fabric.
Make sure the edges of the foam are exactly even with the edges of the plywood.
For seat shapes with corners, let the batting pucker out at the corners (it will be trimmed away).
Staple at least 1 inch (2. 5 cm) away from the edge of the plywood.
Repeat this for all corners and then trim away any excess fabric.
Staple at least 1 inch (2. 5 cm) away from the edge of the plywood.
It’s OK if small buckles of loose fabric pop up between staples as they get closer together—you’ll staple them last.
If the remaining fabric buckles are big enough, fold them down before stapling. [18] X Research source
