It was nice that John had so many nice things to say about fiberglass windows, it is to bad however that he really doesn't understand how they are produced. I myself am a sales manger for one of worlds leading manufactures of fiberglass windows . First, what John is referring to is a mold process fiberglass production process. The process however to make lineals for fiberglass windows is called 'Pultrusion Process'. In this process we use glass roving which is like a yarn and glass mat which is like a fabric which is bathed in a polyester resin. It then is pulled through a preshaping process and then is pulled through a heated exacting die. The heated die causes the resin to cure and the completed lineal comes out the other side in a continuous length that is cut to size at the end of the process. This process produces very strong lineal section which is then assembled into complete window frames and sashes.
As for the paint issue Fiberglass windows come prepainted using a high durabilty enamel and not by colouring the material itself. This is because rather than improve colour stability this process gives you very low pigment saturation with could bleach out over time very analous of a stained deck bleaching out quickly and requiring continuous refinishing and restaining. The enamels however have a very high pigment density and thus are very colour stable.
I could ramble on and on here but it would be a lot simplier if you had a look a our companies web site at http:\www.inlinefiberglass.com