DIY Closed-Cell Silicone Foam

Most of us have a junk drawer, full of spare parts yanked from various places, but also likely stocked with materials we bought for a project but didn’t use completely. Half a gallon of wood glue, a pile of random, scattered resistors, or in [Ken]’s case, closed-cell silicone foam. Wanting to avoid this situation he set about trying to make his own silicone foam and had a great degree of success.

Commercial systems typically rely on a compressed gas of some sort to generate the foam. Ken also wanted to avoid this and kept his process simple by using basic (pun intended) chemistry to generate the bubbles. A mixture of vinegar and baking soda created the gas. After a healthy amount of trial and error using silicone caulk and some thinner to get the mixture correct, he was able to generate a small amount of silicone foam. While there only was a bit of foam, it was plenty for his needs. All without having a stockpile of extra foam or needing to buy any specialized equipment.

We appreciate this project for the ingenuity of taking something relatively simple (an acid-base reaction) and putting it to use in a way we’ve never seen before. While [Ken] doesn’t say directly on the project page what he uses the foam for, perhaps it or a similar type of foam could be used for building walk-along gliders.

Photo via Wikimedia Commons

9 thoughts on “DIY Closed-Cell Silicone Foam

  1. Neat video and method. Wondered about the silicone oil when making the molds of stone tile and stones to make decorative concrete stamps. I used and still have a few tubes of Type 2 silicone so wondering how to do with type 2 also (I’ll think about this and post back if come up with something), Have to try the silicone oil thinning method and read into some more what other silicone oil sources are cost effective and local.

    The video also got me inspired to think about way cost effective RF absorbing materials that aren’t only foam like materials for Anechoic Chambers (pressure wave) and Faraday Cages (electric and magnetic waves)… but for sections of circuits to better shield sections of a signal path inside the metal shield. Wondering what other materials can be mixed in and not react unfavorably (or significantly) to attenuate properties.

  2. Hmm. This is a cool thing I guess but what would it be used for? Making your own insoles? Maybe add powdered ceramic for DIY heat transfer pads? I’ve seen this material before but never in anything i’d ever said “man I wish I could make my own.” So…any good ideas?

    1. I was thinking custom cushions for a homemade office chair. Using this technique, you might even be able to vary the density a bit, which could come in handy for making some parts more or less dense.

    2. High temp gaskets and longer lasting gaskets. I originally was thinking RF gaskets since might last longer as the core material say if you wrap in a 325 mesh or smaller screen. They also are great for outdoors use since more UV resistance and longer lasting in general than other foams.

  3. I can see this being handy for a lot of stuff. Last year a friend and I installed mini splits in his house and somehow the drain line wound up on top going through the hole. We had plugged the hole with great stuff. This would have been a lot nicer to get back out. Definitely worth remembering.

  4. Sadly, Ken, the author of the original article and keeper of the website passed away in june ’21. It seems his son is going to keep the site up for as long as possible, but I’m going to post his formula here for posterity & long term security.

    Standard Formula Materials:
    Silicone caulk. Use GE type one, Dap, or other acetoxy cure silicone. The caulk has to cure with moisture liberating acetic acid. This is the one most used for sealing bathtubs and other areas. (Look for releases acetic acid on the back of the standard 10 ounce tube).

    Silicone oil. Used for lubrication of many materials and readily available at hardware stores. I used Super Lube from Home Depot but any will work to thin silicone. (I learned the hard way to not use V M & P naphtha, Xylene, or others as they causes too many problems).

    Surfactant. Any dish washing detergent to lower surface tension.

    Baking Soda. Sodium Bicarbonate.

    Vinegar. Regular white distilled vinegar.

    Weigh out 20 grams caulk, 2 grams silicone oil, and 3-4 drops dish detergent. Stir well to integrate. These steps go together easily.
    Add 10 grams baking soda. (Move quickly but mix completely to prevent voids. This will begin to skin over and release some acetic acid smell but this is normal).
    Add 5 milliliters vinegar and continue to move quickly. (The mix will begin to foam but settles down fairly rapidly. You now have a stable closed cell silicone foam). It will cure externally in several minutes and cure completely in 12 hours. As most caulks perform, maximum strength is reached in 2-3 days.

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