Foam rubber also called upholstery foam, is a great medium for soft sculpture and toy making. It can usually be found at craft, upholstery and hardware stores. When making something that really needs structure foam can be a life saver. Foam based items retain their shape far better than stuffed pieces.
Toys that will receive heavy use like blocks or play cakes are perfect candidates for felt.
On the downside it can be costly and foam can be cumbersome to cut or make the project look too structured.
Foam is sold in various heights but if you can’t find the size you want you can glue to foam rubber pieces together. This can be a little tricky to accomplish so glue pieces first and then cut into shape not the other way around. All that you need for this is spray glue made for use with foam. This is usually sold in the same places foam is sold.
To cut foam you can usually use scissors on foam under 1 inch. But BE CAREFUL!
Foam larger than 1″ will require the use of an electric carving knife also called a turkey carving knife.
Selection of foam rounds from American Felt and Craft.
From cookies, pies, pizza, and cakes I have cut more foam into rounds than I care to talk about I now use the pre-cut rounds and wedges we have cut just for us and sell at A.F.C
How to cut a foam round here’s how to do it:
You will need:
A tape measure
Template of the diameter round you are making
A permanent marker
Scissors
An electric or turkey knife
Foam
Safety goggles (because tiny foam pieces hurt your eyes)
Goggles on let’s go!
Secure the template into place with a few straight pins into the foam to keep it from shifting.
Trace the shape onto the felt with your marker. Mark out a square around your template.
Using a turkey or electric knife carefully cut out the square.
Using a turkey knife cut in as close as possible to your markings.
Finish by making your piece as smooth as possible with the scissors.
When working with felt your cuts do not have to be completely perfect. As they say “Felt hides a multitude of sins.”
OK only I say that… doesn’t mean it’s not true!
~American Felt & Craft ~ Blog 
If you are looking for help in the selection of the correct variant of foam rubber for any project, can I suggest that this site may be worth a look. They have extensive knowledge of the area and are always willing to help.
hi was wondering if you might be able to help. I’m making a dress form out of upholstery foam stacked up together maybe unadvisable but it’s better than you know purchasing all this other stuff when I got this for about 20 bucks and it’s coming out okay. however, I’m stuck on the bust and how to get it rounded. I’d add a picture if I could but it’s already kind of put together stacked up the glue pretty solid. I’m doing okay with like a homemade shaper out of a jar lid anything will help.
Since this piece is meant to be used and covered again and again and it’s made from multiple pieces of foam I would get them to your desired shape using glue and then duct tape around the foam making it more stable and smoother. Hope this helps.