This is a really quick and super simple project tip, yet it is really useful for wood working! Make flexible sanding blocks/sanding pads from rigid foam and sandpaper to sand any round, concave, or convex shapes. Because they are flexible they conform to the shape you are sanding. It is also easier on your fingers when you use the foam pad. You use hot glue to attach the sandpaper to the foam pads!

Supplies

Polyethylene closed-cell foam, 3/4” to 1-1/2” thick. Recycled packing materials (like sheets or panels) are ok and free! If it's too thin you can glue up a stack to get the desired thickness like shown in step 1.
Wall insulation rigid foam (the pink stuff) also works.
For round shapes use pipe insulation tubes or pool noodles.
I don’t use styrofoam, it’s messy, it breaks, and its not flexible enough to conform to odd shapes!
Sandpaper or sanding disks of different grits
Hot glue gun
5" plywood disk
1/4" carriage bolt and nut
Drill press, band saw

Step 1: Sanding Sponges for Hand Sanding

Cut a piece of foam to fit into the spaces you want to sand. Cut a piece of sandpaper (e.g. 100 grit) a little larger than the foam pad. Use hot glue on the sandpaper, and glue it to the foam pad. Don't use the glue gun tip on the foam, you will probably melt the foam. The sandpaper may extend about a 1/4” beyond the foam pad. Curl the edges slightly upwards.

You can also shape the foam pad (e.g. concave or convex bottom) to match the curvature of your workpiece before gluing on the sandpaper.

After the glue sets, use the sandpaper foam block to sand your workpiece. I have found that the sandpaper does not tear as easily when used this way, and it is a lot easier to use in curved and tight places. When the sandpaper is spend, hot glue on a fresh piece or discard the pad.

I don’t know anything about automotive body repair work, but maybe these flexible sanding blocks will be useful for that as well.

Edit 7/10/22: Well, I am doing some door frame repair and repainting in my workshop right now, and what do you know? The sanding blocks are very useful for that job as well :-)

Step 2: Sanding Disk for Drill Press or Drill Use

Cut a 5 inch diameter plywood disk with a 1/4” center hole. Insert a 1/4” carriage bolt thru the center and fix in place with a couple of nuts. This is your sanding arbor for use in a drill press.

Cut a 5 inch diameter foam disk and hot glue to the arbor disk.

Use a standard 5 inch sanding disk or cut your own sandpaper disk, and hot glue to the foam on the arbor. Mount in the drill press and sand away!

When the sandpaper is used up you can glue on a new piece; or remove the foam pad and reuse the 5 inch arbor.

That's it, really quick and easy!