The ICON RV Skylight Inner Dome provides a layer of insulation and reduces condensation forming on the outer skylight. Molded of textured white polycarbonate with a white painted trim. Fits all standard 18" x 18" skylight openings.• Molded of textured, white polycarbonate• Fits all standard 18" x 18" skylight openings• Opening Dimensions: 18" x 18"• Outer Dimensions: 21" x 21" x 4-1/4" Molded of textured white polycarbonate with a white painted trim Fits all standard 18"" x 18"" skylight openings | Icon Technologies ICON SL1818 RV Skylight Inner Dome in White