Retro-illuminated Travertine About this project Using Clearstep a polypropylene cored sandwich panel from CEL Components with specially designed transparent adhesive is used as a substrate for Travertine allowing the light through to highlight the holes in the limestone. BACK TO GALLERY Clearstep by CEL Components is a sandwich panel with a polypropylene core and 0.4mm thick skins in glass fibre fabric impregnated with epoxy resin. BACK TO GALLERY