Measure the width of your queen size mattress. Add between 2 and 6 inches to this measurement, depending on how much you would like the headboard to extend beyond the mattress. Write this measurement down.
Determine how tall you would like the headboard to be. If you intend to rest your back and head against the headboard, measure your seated height from the mattress to your head. Add any additional height you want to this measurement. Write this measurement down.
Determine how thick you would like the foam for your headboard to be. Write this down.
Add 12 inches to the width and height of your headboard. This will be the yardage for the fabric and the batting. The batting will be two layers thick. If your headboard is short enough that one layer of batting can be folded over, use this measurement. Otherwise, double the measurement for the batting.
Purchase the materials you'll need based on the measurements you've noted.
Draw the desired shape of your headboard onto the plywood, and cut it out with a jigsaw.
Sand the cut edges of the plywood.
Lay the foam on a flat, clean surface, and lay the plywood on top of the foam. Trace the shape of the plywood onto the foam, and remove the plywood from the foam. Cut the foam with an electric carving knife or scissors.
Follow the instructions on the adhesive spray can for gluing the foam to the plywood. Allow the glue to dry.
Lay your chosen fabric on a flat, clean surface. Lay the batting on top of the fabric.
Lay the foam and plywood on top of the batting, with the foam face down.
Center the plywood and foam so that there are 6 inches of batting and fabric around it in all directions. If your fabric has a pattern, center the plywood and foam on the pattern.
Fold the fabric and batting over the top of the plywood and foam. Insert two staples to secure it. Repeat this with the bottom and then each of the sides.
Pick up the headboard and confirm that the fabric is laying the way you want it to and that the pattern is centered if your fabric has a pattern.
Lay the headboard back down. If you are satisfied with the way it looks, continue stapling all the way around the headboard, alternating between top and bottom and the sides to keep the fabric even.
If you are not satisfied with the way the headboard looks, remove the staples, readjust the fabric, re-center the plywood and foam, then repeat the stapling process.
Trim away excess fabric and batting.