In most of the material I have read, including Nick's book, the timbers recommended are Western Red Cedar, and other species from Northern America. These are all prohibitively expensive here in Australia. At least on my budget. Enough Western Red is A$650.00, just over a weeks pay. Most of the timbers we have commonly available here are very heavy(most of our hardwoods won't float), but heaps strong. Most of our softwoods are harder and heavier than the hardwoods I've worked with from Nth America. In order to save weight, how thin can you go with the strips? If the timber has enough strength, could I safely go down to 4mm (5/32")? I realise that the timber is there to space the inner & outer layers of glass apart to gain strength, how strong does the timber have to be? There is a species available as an experimental crop called Paulownia. It is extremely light, about .28 specific gravity, but very soft, something like balsa.