It is important to use backing rod when sealing joints as it is only when the joint materials are installed as specified that the joint will perform in accordance with its advertised flexibility.
Open Cell (usually orange or grey) backing rod has several advantages over Closed Cell (usually white) backing rod. For example;
It is more pliable and so fits into a greater range of joint widths for any given diameter
The open cell nature allows air through to the reverse side of the sealant which improves curing time
However, it also absorbs moisture. Therefore if there is a likelihood that the backing rod will get wet before it is installed and sealed it should not be used – use closed cell instead. Backing Rod Open Cell
Standard sizes: 10mm x 210m 16mm x 150m 18mm x 120m 22mm x 150m 29mm x 60m 30mm x 60m 38mm x 30m 40mm x 30m 50mm x 20m
Backing Rod Closed Cell Standard sizes: 6mm x 50m 10mm x 50m 13mm x 50m 15mm x 50 20mm x 50m 25mm x 50m 30mm x 50m 40mm x 2m 50mm x 2m