# PU/PIR poly vs PVC foam



## 7665 (Jun 9, 2014)

I may be wrong ( and that’s okay with me) but is this the blueish foam? I was at the discount fiberglass store yesterday getting some pvc foam and asked about the other foam. Jesus (store owner) said it is not as hard as the yellowish ( divinycell /carbon core pvc) foam even though it was a similar density. Again, I could be wrong


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## firecat1981 (Nov 27, 2007)

You might want to look into PE foams, like ones from carbon core. Several of the builds going on on this site right now have been switching to that as a great core that won't kill your budget.


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## Indoman (Jul 25, 2013)

Had planned to use the PE but per Tommy it’s out of stock and he is not sure if/when they will get more. I’m not opposed to using PVC, I just noticed the PIR was even cheaper than the PE. If PIR will perform as well as PE for 40-50% less I’m in.


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## Indoman (Jul 25, 2013)

spinnb7 said:


> I may be wrong ( and that’s okay with me) but is this the blueish foam? I was at the discount fiberglass store yesterday getting some pvc foam and asked about the other foam. Jesus (store owner) said it is not as hard as the yellowish ( divinycell /carbon core pvc) foam even though it was a similar density. Again, I could be wrong


Could be. But I would think if they are both the same density....the hardness would be the same?? Or maybe my understanding of the relationship between density and hardness is incorrect.


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## Finsleft258 (Oct 7, 2018)

Indoman said:


> Could be. But I would think if they are both the same density....the hardness would be the same?? Or maybe my understanding of the relationship between density and hardness is incorrect.


Density refers to the mass per unit of volume (how squeezed in it is) while the hardness you're referring to is the rigidity of the product--essentially how stable its structure is and how much it resists deformation.


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## Sublime (Oct 9, 2015)

Just a word on the basalt. If you go with the 350 gram, make your edges really rounded and use resin thickened with cabosil to help it keep from lifting up. I'm using 300 gram and still had issues starting out.


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## firecat1981 (Nov 27, 2007)

So I actually have a sample box from carbon core that has all 3 foams in it.










Below are the 3 foams. #4 is the PE, #5 is the PVC, #6 is the PU/PIR foam.

The PE and PVC are similar in rigidity and compressive strength, the only visual difference is the PVC has a more open cell structure where the PE is much tighter. Both are stiff and strong enough you can't push a finger into it. 










The PU/PIR feels like cheap styrofoam and I can easily push my finger into it. Also where the PE and PVC can flex, the PU/PIR snapped instantly. You can see the grain structure below. I would steer clear!


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## Sublime (Oct 9, 2015)

Excellent @firecat1981 . I'd vote for the PVC. I'm using the PE 80 and I feel the more porous PVC would give the resin more to hold onto.


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## GaG8tor (Jul 8, 2019)

Good info


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## bryson (Jun 22, 2015)

Usually you'll find a correlation between density and strength/stiffness when looking at foam, but density doesn't directly impact anything.

You will also get more strength/stiffness by increasing the core thickness, all else being equal. Impact resistance doesn't change, though.

I would also be concerned with how these products bond to your resin system. I don't know very much about some of the other foams out there, but I know that PVC foam has been used with good success.

Look at the material properties for each, and decide what works best for you. For example, the Carbon Core PVC 60 (~4 lb/ft^3 density) is stronger and stiffer than some of their slightly higher density foams. It has less elongation before breaking though, but with e-glass or basalt skin I don't think you'll be able to take advantage of that anyway.


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## firecat1981 (Nov 27, 2007)

Sublime said:


> Excellent @firecat1981 . I'd vote for the PVC. I'm using the PE 80 and I feel the more porous PVC would give the resin more to hold onto.


I would go with either the PE or PVC. I think the PE has better sheer strength if memory serves so that would make up for the less porous surface, and make for a slightly lighter build with less resin use. If using epoxy either will be great.


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## firecat1981 (Nov 27, 2007)

They have good info on their site for all the products.

http://www.carbon-core.com/products/carbonfoam-structural-foams/pe-foam/


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## Indoman (Jul 25, 2013)

Great info firecat! ....and everyone else. Will stay away from the PIR.


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## Guest (Mar 12, 2020)

Indoman said:


> Great info firecat! ....and everyone else. Will stay away from the PIR.


Yep, what everyone said
The pvc and pe foams are pretty close in price from CC so if they have the pvc in stock and your ready to build just run with it.


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## Guest (Mar 12, 2020)

Oh, the pu foam is just that... polyurethane foam. Good for cooler builds, insulation, even good for shaping a plug prior to to fairing/glassing/finishing.


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## FrankZinCLE (Jul 11, 2019)

Thank you all for going into details here and sharing all of this ... I was looking for an alternative for the Carbon core pvc but it’s clear that’s there really is not one! So I’ll be purchasing the Carbon Core PVC in 16mm(2 sheets) and the 25 mm (1 sheet) for the deck on my 12 for MFG project skiff build


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## DuckNut (Apr 3, 2009)

Tip for making flat panels or a non stick wet out board.

Go buy a sheet of the blue foam from the big box store. Mist it with silicone spray and wipe it around to lay up flat panels. It has a plastic film on it and it is really smooth and you will end up with perfectly smooth pieces, not to mention it is cheap as hell. Also when wetting out you won't run into soak through as you do using cardboard.

Edit: this is for epoxy use. The styrene in poly will still take a toll on the foam through the plastic film.


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