Most of the non-metal material F0 between 2% to 5%, which translates into a Specular value of 0.25 to 0.625. In other words, when making non-metal materials, the minimum Specular should not be lower than 0.25. Water Specular parameter is 0.25, most of non-metal materials (glass, plastic, etc.) Specular value is about 0.5, gemstones, jade Specular parameter can be set to Specular=1.