My first attempt at a portable layout – Granite Rock – used a very conventional pine frame topped with MDF sheet. The backboard was more pine, with a ply backing. It was strong but weighed a tonne. It did the job, but I always risked damaging the thing whenever I moved it because it was so absurdly heavy.
Since then, I've been interested in using extruded foam for lightness, and was especially interested in the uses the Americans make of it. I ended up building a small N gauge “play” layout for my kids about 1600mm by 1200mm that used nothing but foam other than for the track bed. I used the American technique of making a frame about 100mm deep by slicing up one sheet of foam into sufficient lengths to build a frame, and then topping that frame with a second sheet. The result? A baseboard for a layout which was strong, stable, rigid and very, very light. There was absolutely no need for any ply topping or any other form of frame – aluminium or timber or whatever. However, it could probably do with a sheet of thin styrene or aluminium around the edge of the board, simply to protect it from possible punctures.
Points were hand thrown, so I didn't need to worry about a secure base for things like point motors, but had I used them, I’d hardly have covered the whole frame with a sheet of ply just to do that – I would have used small squares just big enough for the job, glued to the underside of the foam.
Ten years later and I’m building a new layout, which at this stage is really a “proof of concept” for a few other techniques I want to try, so this one does have a sheet of extruded styrene on an aluminium frame (Capral’s wonderful Qubelok system). My motivation is twofold: to see if I can avoid timber as far as possible, and to make something as light as possible but is a little more robust than my first styrene baseboard. And the reason for that is that my eventual layout I want to build will be ceiling suspended, to make the most use of my single garage. Hence, something light is important.
Interestingly, I bought the styrene for my original layout from the same place as the one I've just started, but they are not the same product. Ten years ago the stuff I bought was Dow’s “blue foam” whereas the material I’m using now is called Foamular and is pale yellow. I could be wrong but my recollection of the blue foam was thinking it actually did not need a lot of bracing, but that’s certainly not true of Foamular which feels a bit denser than the blue foam, but is also more flexible. So the Foamular definitely does need some bracing, which is what I have done with the aluminium.
How the material at Bunnings compares I don’t know, since the last time I was at the Oxley store it hadn't yet arrived.
I think for many people using foam has a number of advantages: it’s light, it’s strong enough for the purpose, it’s easily worked, it doesn't need power tools to cut, and in a climate like Brisbane’s there is no need to worry about warping over time. Cost wise I’m not sure about the comparison, but I suspect the baseboard I’m building now will not have cost anymore using foam and aluminium than buying good quality timber.
I very much doubt I will use timber in any future baseboards except for very small applications like point motor mounting plates, and even then that could just as easily be aluminium.