uPVC 300mm Soffit Board (10mm General Purpose) 5m - Black Ash Woodgrain Dimensions Length: 5m. Width: 300mm. Thickness: 10mm. Material: uPVC. Guarantee: 10 years. Description The range of solid general-purpose boards (GPB) is a popular choice for soffit applications. GPB products are 10mm thick and are available in widths of 100mm to 600mm. The wider products are particularly useful for deep soffit applications or large box-end construction. GPB products are available in a wide range of solid colours and woodgrain finishes.