Does foamed PVC have a grain?

Although this question will not be of much value to most people, it is certainly of interest to those few .. like myself .. who work with this material. The answer is .. yes, it does .. and this has a significant bearing on how one can get the best out of it! I have to confess that even though I’ve been using it for years, I’ve never properly realised this until now. There’s hardly any visible indication and although I had noticed at times that cutting in one direction seemed slightly harder than another I didn’t attribute a cause. I’d always assumed that sheet plastics just don’t have a ‘grain’, or rather a directional difference, because of the way they’re made and this would be especially so with foamed materials. In all these years I’ve never noticed any reference to a ‘grain’ in any of the product information available .. until now.

I should point out that I’m going on the basis of the tests I’ve made with the brand I use, which is Palight and Palfoam foamed Pvc manufactured by Palram. But I’m assuming that the manufacturing process for foamed Pvc will differ very little between the various brands even though there is often a difference in hardness. After looking more closely at the manufacturer’s documents available for download, I found this tucked away in some notes entitled ‘Installation’:

‘Palight is manufactured as an extruded foam PVC product with a directional grain running the entire length of the sheet. This manufacturing process gives Palight greater flexural strength in the direction of the extrusion. The grain of the Palight should always be installed perpendicular to the fastening point.’

In other words if a thin strip is cut along the direction of the grain this will have more rigidity than the same strip cut at a right-angle to it or ‘against’ the grain .. just like wood! To test this, amongst other things, I first had to find a way of recognising the grain direction, because as I’ve said .. it’s hardly noticeable when looking at the surface or the cut edges! If you hold a piece of Palight up to the light (better still a light that’s glancing the surface) and look at it closely, then rotate the piece 90° and look again, you may just about discern a faint direction of surface texture in one of these views. Another test involves making an indented line with a metal point, such as an embossing tool, a nail or a compass. Along the grain progress will be fairly smooth and hardly make any sound, whereas against the grain there will be a higher, scratchy sound and the surface will resist a bit more. A third test just involves cutting a strip, and is perhaps more noticeable in the thicker versions of Palight. I tested with squares of 1mm, 2mm and 5mm Palight, cutting strips just 5mm wide, first along one edge of the square and then the other. I made sure to keep my exertion with the knife roughly the same, and I found that I consistently needed a couple more strokes to cut against the grain. These strips were also noticeably more bendable than those cut along the grain.

So, I’ve already implied the possible advantages of utilising the grain direction and I’m guessing that the following will apply to all thicknesses .. having tested 1mm, 2mm and 5mm with the same results.  Thin structures will be stronger if the grain follows their length, and they will also be easier to cut! If strips are intended to be bent, this will be easier if they’re cut at a right-angle to or ‘against’ the grain. Finally, and as I’ve illustrated in my page ‘Palight’ brand foamed Pvc under constructing in the Materials section, Palight can be scraped with sandpaper to simulate a wood-grain surface and this will be easier following the actual grain of the plastic. Pvc can also be embossed, ideally using a smooth-pointed embossing tool, and a slightly different quality of line is produced either with or against the grain. You’ll have to try it out, to see which you prefer.

2 thoughts on “Does foamed PVC have a grain?

  1. I realize that you and your reader are speaking about the extrusion grain of the product, which you answered very well (thank you for that). One quick note though, in case someone might be looking for a wood grain surface texture, I realize you’re located in the UK, David, and i’m not sure if it’s available there yet, but at Palram Americas, we make a product called “Palight Woodgrain” ( Palight Woodgrain features an embossed woodgrain texture. When digitally printed or painted, it looks excellent. This product is a spin-off of a wood-replacement product we make that used for exterior trim on homes, Palight Trimboard. If you or your readers have an interest in Palight Woodgrain, please inquire with your local supplier. It may take time, but I suspect we can find a way to introduce it there.

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