Ah XPS foam. The source of confusion for so many new hobbyists.

There's a good reason for this. It's the sort of thing that varies in where you might find it between countries, and is found most cheaply (most often) at hardware stores and builder's merchants - and even there it's not exactly an easy to find pedestrian product.

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There are a ton of different places you can find this stuff depending on where you live, so firstly, here's a basic outlay of what it is and what to ask for in your local area. 

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The proper name for this foam is Extruded Polystyrene (NOT expanded polystyrene*), often abbreviated as XPS. It's most commonly sold as insulation for homes and buildings.

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*this is the white foam made of little messy balls used for packaging - this does have uses but not for most of what we do :)
 

Tons of brands make this product and the brand names, and quality of the foam vary depending on country:

DOW (generally blue) and Foamular by Owen Cornings (generally pink)are the most prevalent in North America, with the owen cornings stuff generally seen as superior for taking texture. One of my US patrons (Thanks William!) also notes that there are different grades of OC pink foam, and you need to get at least 250. He ALSO mentioned more recently that US foam from these sources seem to think '1 inch' is more of a guideline than an actual rule, and it may be anything from 3/4" to 1 and 1/4"! Worth bearing in mind. Especially as the BMC source below is much more accurate.

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The US (and Canada soon, apparently) now has access to styrodur quality (see Germany's foam below) foam thanks to Jeremy from Black Magic Craft! He works with an XPS company with an online store here to provide high quality, smooth foam that takes texture well and makes excellent rocky terrain. It's slightly more expensive than the stuff you would get at the hardware store, but is higher quality. if the texturing of the cheaper foam is letting you down, try this stuff :)

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In the UK the grey stuff I use seems to be called Ravatherm, which (aside from the useful colour) seems to take texture well, but suffers from increased grain and 'furriness' when snapped. basically its not as smooth or good for using for rocks and such. there is also blue and green foam, but I can't attest to its properties.

 

In Germany (and sometimes available in surrounding regions) we have Styrodur (3000 is the one you want). generally seen as one of the best brands of foam, its silky smooth, takes texture well and can be compressed far more than US foam, being less elastic. You CAN get this in the UK, its just not reliable and comes in messy, fused boards that don't even have parallel facings, so...yeah. I used it still, but only for projects where it's more valuable (carving stone and rocks)

 

In Australia there are two main brands, the yellow knauf, and the green bastion. Knauf is basically Aussie styrodur, I had a patron kind enough to send me a sample of both and I did some testing. Bastion on the other hand should be avoided if at all possible, its even more granular than the uk foam and all but crumbles when you try and texture it. it's probably the worst foam I've seen. I'd imagine magnets would pull out constantly too due to its weak structure.

UPDATE: Knauf is being discontinued, grab it if you still can! My Aussie patrons are seeking new quality sources of foam for the benefit of the community, they have some promising leads and I'll post them here when we get some results from testing :)

 

As for the rest of the world, I'm always happy to get small samples and add to this community resource of knowledge! Just message me and I'll let you know the PO box address and thank you profusely 😂

 

In general, the colour is irrelevant and is typically just used as an identifier for each brand. You can find it in pink, blue, green, yellow and probably more. The biggest difference between varieties is density. The denser the foam, the better it takes impressions. Generally each brand makes a variety of densities, but you may only be able to find one or two options for purchase at the consumer level.

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As this foam is sold for insulating houses you will find it sold at building material stores. In places like North America this will be Home Depot, Lowes, and similar. Usually stores will stock just one brand. Also, again you can get higher quality foam from Jeremy at Black Magic Craft here.

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For US sources of thicker 3"+ foam - Just quickly I will mention here (and repeat later below) I have an updated version of the mountainblocks (the main reason to use thick 3" foam) available on my Patreon (mountainblocks 2.0) as a bonus video that DOES NOT REQUIRE thick foam. You can make it from 1" thick sheets no problem. 2" gives you some options with bulges but is far from essential.

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In the UK, I'd recommend getting your foam online from either 4D  or panelsystems. I go into the pro's and cons further down.

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I've also been pointed to the underfloor heating store website. I've ordered a 30mm sheet which I'll strim to 25mm when I've cut tiles on the proxxon, and update this bit if needed. it LOOKS like it might be a nice mid ground between 4d and panelsystems - but we'll see!

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You can also get non-grey foam (unsure of its quality) can be bought online at the Underfloor Heating Direct and the Insulation Superstore websites. These sources also sometimes come with foil attached which you can remove with a bit of effort and damage to the foam, but generally I find it easier to source online from 4D or Panelsystems.

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In the UK it's also harder to get it in the half inch variety, so I mostly use 25mm (1") thick or thicker and cut it down if needs be. You can however, get 10mm foam, which is the perfect thickness to make 1/2" floor tiles with two layers of chipboard - without needing a hot wire to cut a strip from the bottom. Handy if you don't use magnets.

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Finally we have Foam from the Netherlands, kindly linked to me by someone (whose message I cannot find to name them! thank you!)

 

Generally a good place to start is a local building supply/DIY store. if you use the correct name (extruded polystyrene insulation foam', they have the best chance of pointing you to the right stuff. Some places still might not have it, or might have it covered in foil, which is less than ideal (but usable).

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Another option is searching online locally - this is where using the proper name is usually far more successful than in store, as search engines can recognise terms that local shop assistants simply might not know in all that much detail. generally buying online comes with a delivery cost, so its better to buy in bulk, though of course you wont necessarily know the quality of the foam until it arrives. In these situations it can help to at least try to message the shop or even call up and ask details, like does it have a smooth finish or a rough one, is it foil coated, etc. This might not work, but is always worth a try!

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Something else to bear in mind is that this product may be harder to find in more temperate climates that don’t need to insulate for extreme cold or heat, and may be regulated in some areas and harder to find (example California). In some regions where it is not common as wall insulation you may find it sold as an underlay for flooring.
 

It is made and sold in a variety of thicknesses, commonly from 1/4″ to 4″, but again this availability will vary by region. It’s quite common in colder places like Canada and northern USA to find multiple thicknesses available at Home Depot but in other regions you may be limited to just 1″.

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In metric countries, its generally sold in metric conversions of that, so 25mm, 50mm, 75mm etc, though it rarely comes in half inch for obvious reasons - metric sucks at division. I generally buy 25mm and trim in half for half inch tiles. It's probably a mm off, but if they're all the same this barely makes a difference. Its useful to cut these on the lowest possible temperature when doing this to eat up as little foam with heat as possible! One of the reasons I advise a proxxon over other cheaper versions!

 

My main foam (2ftx4ftx1" boards) I picked up from 4D a while back. This version comes without foil, has smooth edges and a smoother finish than other UK XPS I've found, so although it's more expensive. I used to consider it worth it for quality and ease of use, but more recently I got delivered a batch of 25mm that was more like 22-23mm, and useless for splitting in two for half inch tiles or using for temple blocks. so I'm revising that opinion to - just get panelsystems. unless you want super smooth xps for cutting rocky shapes - see below.

 

I also bought another batch, from panelsystems. cheaper, BUT - 4 out of 6 sides had fuzzy, almost furry edges - including the large flat edges! Luckily I'd bought 4" thick foam as an experiment for a video so I can just trim it without losing too much. so you have to buy thicker and trim. it's still cheaper, but its also more grained and less smooth than the 4d stuff when cut.

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You can get this stuff in 3" thick and thicker from either place, which can be useful...

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For smooth XPS in the UK, I used styrodur for my updated mountainblocks bonus video, but I've also picked up some kingspan greenguard to test. I picked up the super high compression strength stuff which is...interesting...to work with. VERY good for texture on the large flat faces, but AWFUL and soft on the edges. Easier to get in the UK than styrodur though, and is roughly as smooth when cut with a knife.

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NOW, for the US sources of thick foam - Just quickly I will mention here I have an updated version of the mountainblocks (the main reason to use thick 3" foam) available on my Patreon (mountainblocks 2.0) as a bonus video that DOES NOT REQUIRE thick foam. You can make it from 1" thick sheets no problem. 2" gives you some options with bulges but is far from essential.

Just thought I'd mention it :)

 

If you do want 3-4" foam online seems to be the best option same as it is in the UK. I've found a link here that will deliver to the UK, so it sure as hell should deliver to you guys!

https://insulation4us.com/collections/rigid-insulation/products/owens-corning-foamular-250-xps-insulation-board-all-sizes?variant=32154942177329

They are sold in large sheets of 8'x4', which means you will need to cut these down a bit and will need to buy a solid sheet at a time, but it's totally possible and still quite affordable, given how long that sheet will last you. You can select thickness on the right.

From the looks of it, it would pretty much cost me the same as my local foam, even with $60(!) delivery to the UK, though you would be buying twice as much at once as I did with mine... Also it's pink foam, not blue, which from what I've heard is slightly better for taking texture and is less fibrous, but this is second hand knowledge coming from black magic craft.

I've also linked the version with higher compressive strength, as I'm presuming that will be the hardest version that should take texture the best and squash the least - though that is theory on my part, I've not had many opportunities to test this theory.

Hope this all helps!