Whirling Sawblades Turn Foam Packaging Into Wall Insulation

If you’re like us, the expanded polystyrene (EPS) foam inserts that protect many packages these days are a source of mixed feeling. On the one hand, we’re glad that stuff arrives intact thanks to the molded foam inserts. But it seems so wasteful, especially when chucking it in the garbage can. If only it could be effectively recycled.

It turns out that it can be, if you equip yourself with this spinning “sawblades of doom” EPS recycler. It comes by way of [HowToLou], who was looking for a way to insulate a wall on the cheap. Almost all commercially available insulating materials – fiberglass batts, blown-in cellulose, expanding polyisocyanurate – are pretty pricey. Foam packing pieces are pretty easy to come by, though, and usually free for the taking. [Lou]’s method of turning them into insulation is a box containing four circular saw blades mounted to a piece of threaded rod and spun by a cordless drill. The blades are mounted askew on the rod for better reduction of the foam; [Lou] chose to use wire to hold the blades down, while we’d have printed up some slanted arbors and bolted the blades down more firmly. A chicken wire prefilter keeps the big chunks from clogging a blower made from an old bathroom exhaust fan, which does a great job of filling the wall cavities with pulverized EPS nuggets. The video below has all the details.

Honestly, the box is a little scary, and we have doubts that [Lou] will be able to get enough foam to finish the job, but it’s still a clever little hack. Grinding things up seems to be a theme for him; check out his leaf collector or his apple cider press.

60 thoughts on “Whirling Sawblades Turn Foam Packaging Into Wall Insulation

    1. Polystyrene foam can have very good flame characteristics. To be certified any insulation has to meet flame spread and smoke development standards, as tested in specific wall assemblies.The pink/blue polystyrene boards sold for insulation meet the criteria, so this COULD work. Changing the configuration to loosely-blown-in PS pearls seems a bad idea because the wall assembly as shown likely hasn’t been tested. https://en.wikipedia.org/wiki/Flame_spread This article mentions that part of the reason PS works well is that heat causes it to melt-and-retreat as relatively non-flammable puddles, which I expect the pearls would also excel in doing.

      1. Also incredibly toxic smoke, regardless of the fire retardants you might add to slow spread of flame through it. And you can bet this stuff is not fire retardant.

        It’s completely banned for construction here in the civilised world, but hey, you wanna make your house into a toxic deathtrap, go right ahead.

        Semi-related: Grenfell Tower.

        1. It’s not banned everywhere, but there is strict process to use it: must be enclosed behind fireproof material (gypsum, concrete), never naked or in dead spaces, must use fire barriers between floors.
          But anyway my insulation of choice is glass whool, at least 40yrs after it was still in good shape in my attic when I put 20 more centimeters on it.

    2. My first thought. I’ve met one firefighter who absolutely loathes it, even in the ‘approved for living spaces’ version. If roofs are insulated with it, it tends to drip down in sticky, scalding hot, sometimes burning globs. A bit like hot glue. Horrible for the occupants of the space.

      It may be nice to reuse the stuff, but i would absolutely choose for glass wool, rock wool or even sheep wool over polystyrene for spaces where people are.

  1. Umm… I hate to be “that guy”, but someone ought to point out that polystyrene is a really dangerous thing to insulate a wall with. It releases *really* toxic, really thick smoke if it burns, and it burns enthusiastically, and it ignites at a relatively low temperature.

    It burns even better if you take big blocks with their relatively low surface area and turn them into smaller pieces with much more surface area…

      1. Yup, and because of that a)his homeowner’s insurance isn’t going to cover him or won’t compensate him in a claim and b)the house can’t be sold until the stuff is removed (which will be, to say the least, invasive) because a house inspector will find the stuff and the buyers will run away screaming.

        The municipality could even condemn the building as unfit for habitation.

        Good job, HowToLou!

        1. Rockwool is the best insulation on the market. No fire spread, sound insulator, protects against the growth of mold/bacteria and is great for thermal protection. Anything else is just inferior for your home

          1. Just don’t inhale the fine dust. Pretty carcinogen if you ask me.
            The question is, can the dust come out of the insulation?
            Under the concrete floor, it is fine (sold under steprock marketing name), but inside drywall, or above your head (eg. around the chimney) it is a big no for me, especially without any vapour barrier (foil).

            So choosing between fireproof and carcinogen, I would rather choose the first.

  2. Worth mentioning is that this will never meet code (at least in the USA, no idea about other countries). Of all of the possible things to stuff your house with, shredded EPS is probably one of the worst I can think of, even shredded newspaper would probably be less flammable.

    1. I know of a company that recycles old newspapers into blow-in wall insulation.
      They do treat it with fire retardant chemicals before pressing it into blocks for easy storage and transportation.
      It then gets shredded on-site right before it’s blown in.

        1. The newer blown in fiberglass isn’t itchy and weighs far less than the paper. A friend and I insulated my attic with the paper stuff and went through a box of face masks between us, were very tired from lifting the bales of the stuff and were covered from head to toe in dust and flame retardant (tastes salty!). A couple of years later, we insulated her attic with the blown in fiberglass, used one face mask each, were much less tired, and were relatively clean. Oh, and the fiberglass is more compact before it’s broken up by the blowing machine, so it took one trip to the store instead of two to haul it.

    2. Correct: long ago, I worked for Philips Components in the film capacitor division. They’re all made from very thin foil.
      We had them in all sorts for all needs.
      When a capacitor had to withstand fire longer than normal, there was paper wrapped in between the plastic foil.
      You have to give this person credit at least for one thing: he tried to save energy, and now it’s published, he has a lot of useful feedback.

  3. I’m not sure what scared me most: the spinning saw blades OR the efficiency calculation.
    But the project is quite interesting and very well deserves the attention. Please forgive me the pun when I say that this is really thinking outside the box. I have no doubts that he will be able to finish the job. Great project!

    Though I really wonder how he removed those small white balls from his clothes. As that could be a completely different project.

      1. hmmm… okay, stupid of me that I didn’t think of that. Now I must think of thime I wasted every time I patiently pulled every white piece of foam from my shirt whenever I worked with Styrofoam. Darn… well learned something today, thanks for the tip. But I’m pretty sure that with my luck it will be a beautiful day with no wind, so perhaps I should check the weather forecast before working with that stuff, haha.

  4. Flammability and mess aside, I’d question the assertion that proper insulation is expensive – certainly I doubt you have to spend very much to achieve a better and more fire-retardant result than this mess.

    1. Depends on what you think is expensive. I put hundreds of dollars of insulation into the 10’x12′ (3x4m) shed I’m sitting in right now when I converted it into an office. When I insulated my two-car garage, the only way I could afford to do it was with the rebates offered by the local power company. Fiberglass batts are not cheap, and foam boards aren’t either.

  5. My dad did this 40 years ago. He ended filling the whole attic 3 feet deep with tiny bits of styrofoam and foam rubber. He used to work for the E.P.A. and hated the fact that although the stuff was recyclable, he could find no-one willing to recycle it, and he knew from his own research how bad it was to throw into the landfill.
    But then a hurricane ripped a corner of the roof off and it “snowed” (in Florida) all over the neighborhood! So much for keeping it out of the landfill!
    Despite that, he kept doing it, and refilled the attic. It was never a problem when it came to selling the house (it has been re-sold 4 times since then because it keeps flooding) and the new owners all liked the idea of all that insulation to save on air conditioning. Just talked to the latest owner a month ago. Maybe I’ll mention the fire-hazard issue to her.

  6. I am surprised of the naysayers here. Don’t americans use EPS in insulation? Here in eastern Europe its one of the most common insulators. Also used for schools and other special buildings. Maybe it is fire-retardant, but it still burns very well. It is also sold as granules for filling cavities and mixing in concrete. Its not the cheapest insulator though. Its mostly used because its waterproof and really easy to cover large concrete walls with. Recycling is a problem though, only packaging material is partially collected and properly handled, most of it gets dumped or burned illegally. But don’t think you can get some leftovers, noo.
    Second point – whatever this man is building, it does not look to be a house. Building a shed etc is generally less regulated.
    Third – I really liked how he tested for insulating properties of the ground-up material.

    I would most likely reuse this idea, only that it is way easier to just buy-ready-made-material than hunt-for-leftovers-and-recycle.

    1. As a filler in hollow bricks, maybe not so bad if there’s a fire retardant in it. But regular styrofoam packing material has none.

      Not many people insulate uninhabitable buildings.

    2. In Eastern Europe, EPS is typically used sandwiched between layers of brick and mortar, so that air can’t get to it. I would assume it is very difficult to get it to burn because there is no oxygen.

      North American house construction uses wooden studs and large wall cavities filled up with insulation:


      There is typically some air there as well. Now imagine wood, air and EPS: it’s a firestarter at the least provocation.

      Why N. A. uses such construction? Cost. By my own calculations, it is 3 times cheaper than the good old brick and concrete construction for the same home surface area.

      1. Well, it’s not just initial construction either. You have to remember that the US has a strong sense of remodeling, rehabbing or retrofitting homes. It’s much easier to add network, multimedia, electrical cables/outlets into these kinds of walls than brick and concrete. I lived in Germany for a few years, and I don’t remember seeing as much industry/interest in home renovation compared to what we have in the US. (Lowes, Home Depot, “You can do it, we can help”, etc.)

        1. I agree with you. However, European homes in general (brick, concrete and mortar) give me much better feeling of solidity and fire protection, than N. A. homes do. Sound insulation is typically better between rooms as well.

          But it does cost more in materials, and it is more difficult to remodel.

          N.A. homes could also probably be classified as more nature-friendly (wood construction, gypsum), if they weren’t 3 times bigger than they need to be. This implies huge energy costs just to heat the dmnd things up.

    3. EPS (expanded) isn’t as common as XPS (extruded), which is extremely common. Most of the naysayers know very little about building codes, and love to sh!t on projects. It wouldn’t surprise me to see somebody post a project using wooden framing on here and have everyone come ‘out of the woodwork’ to cry about how they wouldn’t live in a house made out of matchsticks! A quick google search for EPS building insulation yields TONS of results from actual builders who are safely using regular sheets of white EPS foam.

  7. Hmmmmm… I’ve been thinking about a wood chipper to make mulch out of my copious piles of branches and logs. I’ve used a small one for many years but it is showing its age and doesn’t chip anything larger than 1-1/2 inch, even if it’s rotten. (It mostly goes in the garden.)

    1. I doubt this system would work well (off axis saw blades) I have doubts that using a wobble type dado blade (which would have a better mount/connection to the rotating shaft) would make an effective chipper.
      I used to have a 1.5 inch electric chipper, but it was a hassle feeding the small branches into it (for the volume of branches my trees produce). I bought a larger one gas powered one from a neighbor, but its problem is that it blows the chips out so close to the ground as to rip out the sod.

    2. Honestly, don’t scrimp on wood chippers. I used to have a “real” chipper that attached to the PTO of my 28-hp diesel tractor. That barely managed to chew up 3″ branches. I also had a homeowner-grade leaf-and branch chipper, a Craftsman, which actually did a great job on the small stuff. I used to use the two in series – make mountains of big chips with the PTO chipper, then grind those up again in the small chipper. Double-ground ramial woodchips are the bomb for mulching and composting.

      1. The smaller chippers make great apple maceraters for your cider press though. I can dump a 100 pound feedbag chock full of apples in one end of mine, and it is running just a tad above idle and get 2 5 gallon buckets of apple goop out the other side in under 30 seconds. You need to put the chipper up on a couple of old pallets so the collection bucket can fit under the ejection chute, and you need to wrap the top of the chute and bucket with something as the goop will come out with enough force to hit the bottom and fly out the top, even with the machine just purring. I built an apple musher that used a 3/4hp electric motor and had a 6″ diameter hard wood wheel with teeth to crunch the apples and it was powerless compared to the chipper. A fun build, but really not good for mass production.

  8. As far as insulation goes, my uncle in-law uses the wool from his alpaca when he sheers them. He made some bags out of fabric, fills the bags with wool then tosses them up into his attic.

  9. Please don’t do this. Any building this were to be blown into will eventually be torn down either intentionally or through some natural disaster. Marine life, local wildlife and everything in between do not need billions of tiny pieces of plastic floating around that can be mistaken for food.

  10. Get day old bread free from bakeries (Panera used to donate to a local thrift store near me). Metal, air-tight box. Argon. Heat source. Make carbon foam. Run this through machine. Or bake your own in a silicone-molded tongue and groove shape like the pink foam panels. Carbonize. Flame proof to 6000C.

  11. It’s under $8 for 5 cubic feet of real EPS bead, Google “Shredded Polystyrene Insulation”. The only difference is:
    1,2,5,6,9,10-Hexabromocyclododecane <1%
    Proprietary Polymeric Film 1-3%
    So brominated flame retardant and probably a hydrophobic film to prevent mold.

    So add some to the free method, or maybe install it in masonary and increase a block from R2 to R8. Cover with an appropriate fireblock and it should meet code. (Canned spray foam is a fireblock, go figure, but might only meet code if it's orange?)
    Total when done is cheaper than store bought or even water-proofed perlite or vermiculite (pop-corned obsidian volcanic glass and mica respectively).

    The UK EPS beads include a binding agent that keeps the beads from leaving the wall, but most people in the US just insulate on the inside or outside and not between for better quality (thermal bridging).

    Electric mulcher-shredders are cheap, hand-held is $40 for a cheap leaf and stick plus blower, or $100 for a 15amp 1.5" branch. You need to ripe up styrofoam but multiple uses for the mulcher.

  12. Here’s the problem with this stuff – it’s like almost lighter than air – so cleaning it, sweeping it, handling it becomes almost impossible. I should know – I’ve spent a week trying to clear it out off my garage attic. Now, as long as once it goes in to a space you need never enter that space again, and the concerns with the fire hazard notwithstanding – then OK, I guess. But I curse the previous owner for using this stuff in an attic where he obviously intended access (due the the drop-down staircase leading up to it). Had an issue one winter where my roof blew a leak, water froze and broke through the drywall ceiling and the entire garage was covered in the stuff. So my bad not being on top of the roof but the mess this stuff created made the job 100 times worse. It would be much better packed in bags (that won’t rip’ and used that way – but loose? May I never see the stuff again!!

  13. What a clever idea for repurposing EPS foam packing peanuts! The ‘sawblades of doom’ concept is undeniably entertaining.

    While the cost-effectiveness is certainly attractive, have there been any tests done on the R-value (insulation effectiveness) of this recycled foam insulation compared to traditional materials like fiberglass batts? Richmond General Contractors

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