These packers are designed specifically for use with the Blue 60 PU Foam to allow the foam an even surface during expansion, and prevent the foam flowing out under its own weight. The strips are available in 1mm (green), 3mm (white) and 5mm (blue) thicknesses to suit gaps between 7mm and 30mm. A typical door set will require around 33 packer strips (depending on the gap width). When used in conjunction with the Blue 60 foam they will provide up to 1 hour fire protection on timber doors.