# polyisocyanurate foam as core?



## weldandglass (Sep 29, 2009)

Hull construction...I wouldn't. These types of core, similar to XPS cores, have high friability and low peel strength. 

If you take your finger and rub these types of foam core very hard, you'll notice they have a tendency to crumble or give way. Do two test laminations: one on your polyiso core and one on a conventional PVC core like airex, corecell or divinycell and then try to peel the laminate off of each. You'll see that the polyiso core laminate can be peeled off much more easily. This is because of low peel strength.

Some builders are using these cores, in higher density and greater thickness, for transoms. I think that the foam between the sole and hull on a carolina skiff is a polyiso core, but in much greater thickness. I've used these cores to build temporary molds for hatches, because they are very easy to shape. One you start cutting on them and working with them you'll develop a feel for why it would not be suitable for use as a hull core They have their purpose, but not in hull construction. If you look around on the internet you'll find where people have tried to use high-friability, low peel strength cores in hull construction and what resulted was a fairly temporary boat.


----------



## Guest (Jun 9, 2018)

Great core for a fiberglass cooler build!


----------



## yobata (Jul 14, 2015)

@weldandglass and @Boatbrains what about using this foam for a stand up paddle board? I don't imagine a SUP goes thru the same forces as a skiff hull...


----------



## Guest (Jun 11, 2018)

Maybe ok for an sup, not sure it’d work for a surf board though. I’d be willing to try it for low stress projects.


----------



## weldandglass (Sep 29, 2009)

Yobata,
It's my understanding that the polyiso cores have very similar mechanical properties to the XPS and EPS cores, which are, in fact, used in surfboard construction. As such, I think they could be suitable for SUP construction as well but I can't find anyone whose actually using them on the internet. I'm an advocate of test panels. Cut a 1ft by 2ft piece of the polyiso foam, shape it as you would if you were building a surfboard or SUP, laminate it, then torture the crap out of it and see how it holds up.


----------



## weldandglass (Sep 29, 2009)

I should add that I like to use a hammer to torture test panels. You can strike the panel while it's lying flat on the ground with both the claw side and flat side of the hammer. The claw side gives you an idea of puncture resistance and the flat side of the hammer will show you the compressive strength of the core/laminate matrix (how much it crushes) and whether the laminate plies delaminate when under a compressive load. You can also cut your test panel into thinner strips and bend them by hand to see if the plies delaminate from the core under bending loads.


----------

