Creating expanded foam from non PS plastic

Has anyone tried to make expanded foam pieces for flotation devices? Something to make a small floating dock for rowboats? It wouldn’t have to be perfect. Just have enough trapped air to make it float. Having a single air pocket might make it subject to leaking however.


I’m interested in creating custom foam shapes. My need is mostly for martial arts training equipment and low-cost crash mats. Neither is easily available in the general retail market. Niche products are always ridiculously expensive.
I’m currently buying off-the-shelf products (like pool noodles) and then cutting and pasting them into the shapes I need. But this creates a lot of off-cuts. So, I’m wasting a lot of material that I can’t do anything with.
It would be great to create only the amount and shapes that I actually need. Even better if I can make it from recycled material.



Yeah, plastic welding and plastic smithing, techniques well worth experimenting with….

So why not Foam?
We both don’t have the setup to be able to experiment, but maybe somebody is willing/stupid enough to try to extrude with added CO2, just for the fun of it?
Realising Whipped Plastic will give you bragging rights!
(at least in my book)

There is at least one manufacturing process where pool noodles are extruded. So, I’m curious about what’s happening inside the machine.
If you can make one shape, you can make many. LDPE foam is also extruded in a “net” configuration that is used to package individual large fruits like mangos (see the photo below).

The hardest thing to find at reasonable cost, is foam hand grips. I buy children’s skipping ropes at a toy store and take off the grips. I keep the rope just for rope. The plastic handles are left as “waste” that needs to go for recycling.
But I can only collect so much rope, before it’s ridiculous. I’ll keep looking for a practical solution.
So, I think there is hope for the concept of DIY impact foam. It’s something for developers to look at.

There’s also this trick to try:
Heat welding polyethylene foam (with a heat gun)
It might just be very tricky with tiny pieces and I don’t know how to identify the difference between PU and PE foam. I guess you just test it, and see if it melts or burns. PU is apparently very heat-sensitive and basically just dissolves like cotton candy.

Thanks for the links, thay also made me find this video:

It’s suposed to show how to recycle PET into foam, but also says “only 15% of recycled materials is used, because otherwise you get ‘bad foam’”.
Back to the drawing board!
It appears most of the time the airpockets are created by CO2, which does make me wonder what would happen is you add bakingsoda and vinigar to a plastic mix, or if you could use a ‘whipped cream’ kind of way to spray plastic in a mould…

As for the chip-foam:

They indeed use ‘a binder’.
For me these ‘mats’ are useful as arrowstops, but so is a container stuffed with palletwrap.
For your uses you could of course mix and match hard and soft PU-foams to get the consistancy you like in a mat. Cut a too soft matrass in half, add a layer of hard foam, repeat until happy. But like for me, I think there are better alternatives…


Thanks, @donald
Here are some basic demos that explain the concept:
Rigid Foam molding
Factory production process
Soft polyurethane tutorial

Yes, the standard method of production is clearly a chemical reaction. I thought it might be a mechanical process (like injecting air into a vat of liquid, or something like that.)
But one of my pool noodles says it’s LDPE (Type 4). So, same chemical process? I wonder.

Anyway, finding a cost-effective alternative to off-the-shelf products seems unlikely. For small-scale production, at least. Unless someone can come up with an entirely different alternative material with the same basic, physical properties.

The multi-coloured or “speckled” sheets made from joined waste pieces (seen in the video previously posted) is called “chip-foam.” It’s quite stiff and would typically be used as the bottom layer of a crash mat or core layer of a gymnastics mat. I find falling on it, even from standing height, still hurts quite a bit. The type of floor under it might make a difference. Hard wood and concrete will hurt. I’ll try to find out how they are joined. The surface is quite brittle and one can break little pieces off of it with one’s fingers.

There is a spray-can adhesive that sticks PU foam pieces together. That might be a way to salvage off-cuts.

Allright, did some digging and all expanded foams (also non-PS) seem to be made to ‘foam’ chemically. I however also found this video als showing the kind product I was looking for:

They appear to simply ‘remould’ cut-up foam into new shapes…
Could also be our solution…

As a bonus:
PU foam, so a bit off topic, though technically it’s also ‘non-PS’ 😉


You are right, these links mostly involve EPS, which was NOT the question. Sorry about that, though they might give some insight into the processes involved in making foams.

I am also looking into foams for creating archery targets, which have an even higher density of what you’re looking for, though they may be the same material, onlu molded under an higher pressure.
I’ll look into it further (later) this week, ’cause now I’m also curious 🙂

Thanks @donald
I haven’t even begun researching the materials yet. I’ll look into it. But I’m not a “techy”.  I’m mostly here to just watch, learn and copy.
The foam I’m talking about is open-cell foam. Soft, spongy, squishy material that acts as a shock-absorber.
It might be a completely different material and manufacturing process.
I buy sheets of the stuff from a local mattress factory. It helps to combine different densities in layers. That’s what makes a good gymnastics mat or mattress. It affects the “impact profile” of the foam to reduce how much the impact hurts you.

@joe-mama @frederikc

Does this link help?:

Expanded Polystyrene Foam

There’s also these topics on the forum:

V4 Styrofoam Workspace [cutting/shredding]
V4 Styrofoam Workspace [melting]