How to use expanding foam

Updated February 21, 2017

Use expanding foam to make moulds, toys, boat flotation, sound proofing, packaging foam and insulation. Chemically resistant, urethane foam cures or hardens in about three to seven days. When it has cured, you can choose to sand, paint, stain or carve it. Expanding foam comes in two parts, and a 7.6 litre (2 gallon) kit fills about 0.23 cubic metres (8 cubic feet) of space. You can also purchase expanding foam in different densities of hardness and in spray, gun applicator and prepackaged forms. Find expanding foam in hardware shops or online.

Make a batch of expanding foam

Adjust the temperature if necessary to about 23.8 to 26.6 degrees C (75 to 80 degrees F), or a temperature you feel comfortable wearing a T-shirt in. Cooler temperatures cause the foam to rise and then shrink, making the foam unusable.

Put on your rubber gloves and protective clothing. Never mix expanding foam without wearing protective gloves. The only way to remove expanding foam requires sandpapering your skin. Also, expanding foam does not come out of clothing.

Spread out a plastic bin bag over the surface you will mix the expanding foam on.

Pour can "A" into a measuring cup in the quantity you desire.

Pour can "B" into a separate measuring cup in an equal amount as can "A." The ratio is always 1:1 or 50 per cent of each solution.

Pour the measuring cup with can "A" into a third container, like a plastic bucket, scraping the sides of the cup with a spatula to get all of the liquid out. If you do not scrape the sides, you will have inaccurate ratios and the expanding foam will have a lower quality.

Pour the measuring cup with can "B" into the same bucket as can "A," also scraping the measuring cup sides well.

Mix the two liquids quickly and thoroughly for about 30 seconds until it reaches a creamlike consistency.

Pour the expanding foam mixture immediately into the area or space you want filled. You will notice how quickly the mixture expands, which will continue expanding to about 30 times its original amount. Foam thickness, temperature and humidity affects how long it takes to cure or harden.

Use expanding foam in moulds

Grease the inside of the mould using petroleum jelly. Get all of the creases and crevices covered with the jelly.

Attach the mould halves together (if it comes with two pieces) using duct tape.

Mix a batch of expanding foam in the quantity you desire or use a spray expanding foam.

Pour the foam into the mould, filling it 1/2 to 3/4 full. Let the mould sit for three to seven days until it has cured. Separate the hardened foam from the mould. The foam should pop out with ease.

Expanding foam in packaging

Press a room temperature bag of prepackaged expanded foam liquid to open the seal.

Mix part "A" and part "B" in the bag, back and forth a few times. You will notice the bag start to expand.

Put the expanding foam bag inside of the box or shipping container.

Place the product you plan to ship on top of the expanding foam bag.

Mix another bag as you did with the first one, and place it on top of the product. Close the box or shipping container. The product will ship safely cushioned in between the two expanding foam bags.


Spray the interior of a mould with vegetable cooking oil as an alternative to petroleum jelly before pouring in the expanding mould.


Do not use expanding foam outdoors unless you paint it first or apply fibreglass to it. This foam does not have UV protection and will deteriorate.

Things You'll Need

  • Rubber gloves
  • Protective clothing
  • Plastic bin bag
  • Two measuring cups
  • Plastic bucket
  • Two-part expanding foam kit
  • Petroleum jelly
  • Mould of your choice
  • Duct tape (optional)
  • Pre-packaged expanding foam bags
  • Shipping carton or box
  • Item or product to ship
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About the Author

Chyrene Pendleton has been a business owner and newsletter editor for more than seven years. She is a freelance writer with over 25 years experience and teaches a variety of topics, including alternative health, hair care and metaphysics. Pendleton is a certified television show producer, radio talk-show host and producer, and a computer programmer with a bachelor's degree in computer science.