The simplest fabric to understand is a Plain Weave; it's simply over and under in each direction. (That is to say; the weft is carried over all odd-numbered warps and under all even-numbered warps. For the next pass of the shuttle, the weft passes over the even-numbered warps, and under the odd.) Sometimes it's two over and two under. It has the advantage of giving strength in both directions with a 90º bias but the disadvantage of halving the UD strength (since half the cloth is at 90º). Another disadvantage of the plain weave is that the cloth is bent over and under which imparts some shearing distress on the fibres therefore weakening them compared to UD fibre which lays flat. Plain weaves will curve over simple one-way curves but with compound curves there can be a problem. Try pushing some in a mould and you'll find out - you'll end up with wrinkles and will have to snip the cloth here and there if you're not careful. The finest plain weave glass is about 25gsm. (German Plain = Leinwand)

Spectra, the latest in the line of modeller materials, is the lightest material so far with a density of 0.97g/cm³ less than water. It is a long chain polythene chain molecule with a high impact resistance and the highest strength to weight ratio so far. Like aramid fibre it has the drawback of fuzzing when worked on. Spectra is the US name, in Europe it's called Dyneema. If you're into fishing or kite flying you will have come across these two fibres already.