Lower-cost composite base material for pcb's, lying qualitatively below FR4 materials. CEM-1, the cheapest base material, is epoxy resin impregnated, cellulose paper based laminate with only one layer of woven glass fabric on each side. CEM-3 has a core of glass fleece (non-woven glass fibers) with epoxy resin impregnation and woven glass fabric on its outer surfaces. CEM stands for Composite Epoxy Material.