| > I can see why it's a common practice for foam sheets to have a pre-scored grid and come with a attatched scrim skin.

| That is for compound curved moulds, not for flat sheet infusion which only needs 2mm scores. This might be an issue with 3mm so you are probably better off using a flow medium. Soft shade cloth works well.

Interesting. I would guess Bob's model would not come close to stressing the skin shear, which is about impact, and the model is light. And that the melted styrene surface would make the best bonding surface from a molecular point of view.

But Rob has said before that low grit sanding the surface improves adhesion. As does the 2mm (1/8") channels for resin flow.

So, perhaps a surface that is impacted, like a boat hull, needs more of a physical connection to the foam. Which is why the channels, and the large cell of Divinycell foam, work well and why the fine cell of XPS is less effective. The 'deep' channels engage far more of the foam, spreading the impact to much larger volumes of the foam.

Perhaps XPS might be better paired with carbon, as carbons stiffness makes any impingement spread over a much larger area.

I wonder if, given the above, there is a formula for low gsm carbon, and it's resin savings, and 100 psi XPS, to be cheaper than glass Intelligent Infusion? There certainly would be a weight savings.

Also skins on airplanes see very small forces. Typically they can be impinged with a pencil point and the weight of said pencil. In fact most composite airfoil skins are many times stronger than they need to be, for these reasons. Also because you can only get fiber so light. Those pushing for records might not be, and can be damaged by some flying bugs on takeoff and landing.

| > So If I went with a formular 250 1" sheet from Home Depot, hot wire cut it, I should sand the cut surface to open up the pores sealed by the hot wire, am I right?

| Yes

One could argue the solid styrene surface left by the hot wire might be a very good bonding surface.

| > Just to be sure, this is for a scale model use only so nothing critical at play for long term longevity.

| Your call. Do a sample and see.

When you pick up the sheets, Bob, pull a few off the stack and touch the surfaces. See if you notice an oily residue between the sheets or on the surfaces. I have. I think it is to stop the stack from sticking together, and that is a source of many bonding issues. Also notice the XPS has a 'skin' of some sort. There is no 'skin' with typical composite foams.

As styrene is not great with solvents, as they melt XPS, it may be hard to remove this oil. It seemed resistant to soap. It may be silicon based. Perhaps hot wiring off the factory surfaces makes sense.