uPVC 300mm Hollow Soffit Board (10mm)  5m - White Dimensions Length: 5m. Width: 300mm. Thickness: 10mm. Material: uPVC. Guarantee: 20 years. Description Hollow soffit is a popular choice because of its attractive panelled effect and installation friendly tongue and groove profile. The hollow soffit range comes in a choice of 100mm, 250mm and 300mm widths with accompanying trims and ventilation accessories to ensure a neat and professional installation. Hollow soffit is 10mm thick and is available in wide range of solid colours and woodgrain finishes. Hollow rigid products are not recommended for use on external cladding applications.