Heat Shrink Black/Red Kit. This kit contains a selection of black and red heat shrink tubing supplied in a storage case. Heat shrink is a versatile product and has many uses such as protection, insulation and strain relief for cable terminations and connections. The RNF 100 range of tubing has a shrink ratio of 2:1 and a range of sleeve diameters are supplied to suit your application. Features and Benefits. Black/Red. Shrink ratio 2:1. Flame retardant. Flexible. Supplied in useful compartment box