TECHNOLOGY FOCUS - POLYMERS - Preferred Materials: (A) and (B) have at most 0.01 refractive index (Rf). (A) has at least one component with a higher Rf than (B), and at least one component with a lower Rf than (B). (B) has 1.45-1.55 Rf. (B) is a glass cloth. (A) has at least 150degreesC glass transition temperature (Tg). (A) is a crosslinked acrylate resin having (meth)acrylate containing at least 2 functional gps. as a main component (esp. having an alicyclic structure; more esp. of formula (I) and/or (II)). (A) is a cured epoxy resin having an epoxy resin containing at least 2 functional gps. as a main component (esp. triglycidyl isocyanurate structure or having an alicyclic epoxy resin structural component). The epoxy resin is crosslinked by curing with a cationic curing catalyst. Preferred Composition: The composition is a molding in the form of a 50-2000 mum thick sheet. The composition has at most 40 ppm average coefficient of linear expansion at 30-150degreesC. The composition has at least 80% light transmittance at 400 nm. The composition is a plastic substrate for display elements or substrate for active matrix display elements. R1-R4 = H or methyl; X = H, -CH3, -CH2OH, NH2, -CH2-O-C(=O)-C(-CH3)=CH2 or -CH2-O-C(=O)-CH=CH2; a = 1 or 2; b, p = 0 or 1. EXAMPLE - A 100 mum S glass cloth (Rf = 1.530) was baked to remove organics, treated with acryloyloxypropyl triethoxysilane, then a resin comprising 92 pts.wt. dicyclopentadienyl diacrylate (Rf = 1.527), 8 pts.wt. bis(4-(acryloyloxyethoxy)phenyl)sulfide (Rf = 1.606) and 0.5 pt.wt. 1-hydroxy-cyclohexyl-phenylketone (Rf after crosslinking = 1.533; Abbe index = 51) impregnated, degassed, molded into a glass sheet, cured using 10 J/cm2 ultraviolet light, and heated in a vacuum oven at 250degreesC for 3 h, to give a 0.1 mm thick transparent sheet. The sheet gave 11 ppm average coefficient of linear expansion, over 250degreesC Tg, and light transmittances of 85% and 89% at 400 nm and 550 nm, respectively, compared to 16 ppm, 210degreesC, 70% and 89%, respectively, for a comparative example prepared using E glass cloth (Rf = 1.560), 58 pts.wt. dicyclopentadienyl diacrylate and 42 pts.wt. bis(4-(acryloyloxyethoxy)phenyl)sulfide (resin Rf = 1.560; Abbe index = 37).