The 25mm or "Fivewall - Xwall" is the thickest polycarbonate that we supply. It's taken over from the 16mm as the better insulator and therefore has become the more fashionable. Although there are thicker polycarbonate sheets available now eg 30mm and 40mm there isn't really a much greater benefit in its performance with regards to insulation or strength. Again the 25mm is available in different shades. As well as the bronze and the opal there is also the combination Bronze & Opal, (bronze outside, opal inside).