Creating objects out of foam rubber is not as difficult as it may sound, thanks to kits available online from theatrical suppliers. The easiest form of foam rubber to make is called "cold foam," which has all the properties of foam latex but does not requiring baking or curing in an oven. You can mix the foam from the kits and use it to sculpt items and pour molds for things like prosthetic ears or to fill stage props with spongy foam.
Things You'll Need
Canister-type respirator mask
Plastic, plaster or fiberglass mold
Mold release agent
A/B or Two Part Cold Foam Chemicals
Plastic mixing bowl
Mixing bucket (optional, for big batches)
Electric mixer (with extra mixer wands)
Drill with mixer attachment (optional, for big batches)
PAX paints (optional)
Gather all your equipment together in a central work area. This is a very important step because once your cold foam is mixed it must be poured into a mold very quickly before the two chemicals in the mixture begin to set up. You won't have time to organize your tools once the chemical process begins.
Cover the floor and counter areas with thick plastic tarps. These foam products can damage unprotected floors. Don an apron and the rubber or latex gloves. Prop the protective eyewear on your head and have the canister respirator nearby.
Cover the inside of your mold with the release agent. You can use the release agent that comes with the foam kit, or you can use silicon spray-on oil. If you don't use a release agent, the foam rubber product will be impossible to remove from the mold.
Measure the precise number of grams of the Part A chemical as specified in the product directions on a gram scale. When you have the precise amount of chemical measured, pour it into a plastic mixing bowl.
Put on the protective eyewear and a canister respirator unit. Plug the electric mixer in and have it standing close by. Have the mold close by as well, both parts if it is a two-part mold.
Measure the precise amount of the Part B chemical on the gram scale. Pour this Part B chemical in with the Part A chemical in the mixing bowl.
Immediately begin to mix the two chemicals. You will have 15 seconds to mix the chemicals with the mixer before the foam will have "gone too far" to be poured easily.
Pour the chemical mixture into the mold. If it is a two-part mold, clamp the top side of the mold over the bottom side of the mold and bind the mold pieces together tightly. You will only have 15 seconds to accomplish this. If you don't get the foam into the mold in this short amount of time, the batch will be ruined.
Do not touch the mold while the foam is curing. The process takes about 20 minutes to complete.
Remove the top of the mold and pop the latex object out. If the latex is stuck to the sides of the mold, not enough release agent was used. You will have to use a fresh mold for a second attempt.
Trim and paint the mold to suit. Use PAX paints to paint on this kind of foam. Spray paints will eat the foam. Other types of paint won't stick to the foam very well.
Dispose of any equipment that still has foam residue on it. You cannot clean these items and you don't want to reuse them or risk contaminating the next foam batch.
A/B cold foam is sensitive to humidity and air pressure. Don’t attempt to create this foam if a storm is coming in, or if it is raining. The moisture in the air, or in the mold, will retard the foam rising effect or spoil the casting. You’ll end up with a pile of goo.
A/B cold foam is a noxious-smelling chemical and you should not breath the fumes. Do not get any of the chemicals or uncured foam on your skin. Protect your eyes from chemical splashes. The foam is safe once it is cured. Make sure your mold is tightly sealed; the pressure of the expanding foam can cause mold pieces to fly apart.