I needed more high density foam over the weekend so I ended up at Bunnings. Bunnings now list two different brands online at the same price - the familiar yellow Knauf board and a new greenish-blue kind from Bastion. They have slightly different insulation specs, but the descriptions are basically the same (both a extruded, both claim to be 'closed cell,' both are quite tough and very light etc - although Bastion specifically lists 'hobbies' as one of it's uses, while Knauf only lists building applications).
Since the branch I was at had run out of 30mm Knauf, I bought some Bastion. And now I hope they get Knauf back in stock.
Here's why.
 |
| Here's a comparison shot. The Bastion is the blue-green stuff at the top (it's a lot greener than the extruded blue stuff you often see online and can get from Solid Solutions). Both of these off-cuts were cut using a table saw - although not the same table saw. You can start to see that the Bastion has a much coarser texture. |
 |
| These are the sawed edges - note the texture of the Bastion board - it's marketed as being closed cell, but it does have a much foamier, bubblier texture. There are 'bubbles' which lead to a rough texture along cut edges. The Knauf by contrast is pretty smooth and can be sanded back so the cut edge matches the smoothness of the extruded top surface. |
 |
| Here's the top surface. Knauf is nice and smooth, you can see the Bastion is pretty rough. Sanding it does not make much impact on the texure as it's caused by bubbles, so more just open up as you remove upper layers. |
 |
| First test - my traditional drawing hard to make cobble stones. The Knauf takes the indentation nicely with no tearing, and the pen leaves clear marks behind so you can see what you've been doing. The Bastion however... The pen does not roll through the material, it jumps and skitters as it tears it's way through the bubbly surface. This tends to mean no ink is left, and it's hard to see what you've done. (Click for fullsize image - it's not super clear here) |
 |
| Next up, cutting a line with a knife and widening it with a pen. This works much better on the Bastion Foam than just drawing. It's just about as good as the Knauf foam. Note that the rougher surface texture of the Bastion will show through when painted giving a more 'sand stone' look where Knauf's smoother surface works for denser stones such as granite. |
 |
| Finally, carving rocky textures using the cut-and-flick method. The Bastion will just about manage this, but you cannot get quite as fine detail as the Knauf. It also feels a lot more fragile - at full thickness the boards feel almost equally tough (Bastion seems a bit weaker) but when carved into thinner shapes, it's clearly weaker. The detail tends to end up a bit softer too. |
Okay, so conclussions time.
I did not photograph carving stone blocks using the 'V' shaped cut method as it works fine on Bastion. I also didn't photograph adding texture using the back end of a paintbrush and some preassure, or rolling a ball of tine foil. The paintbrush method works okay, but not great, and I have yet to try the tinfoil ball, but I suspect it will not be great as the bubbly surface will likely tear up (it did this to an extend with the paintbrush-butt method).
Bearing all that in mind, it's pretty clear that the Knauf foam is the better option. It carves beautifully, takes texture well and is pretty rugged even when cut thin. The Bastion board on the other hand is a little lighter, and if you don't want to carve it there's not really much of a problem. It would be fine for sand or grass covered modular terrain tiles or hills.
Of course, since both cost the same, it's really just a question of availability. If Knauf is there, buy the Knauf every time. I'm just worried that Bunnings may have changed supplier and won't be stocking the excellent Knauf foam any more. I've had a look online, and Knauf are still in business and their products are available from specialist insulation shops in much larger sheets, so I'm going to be buying online in future if Bunnings continues to fail me.
