Insulation for hot water cylinder (Bradford on Avon BA15)

This is for old hot water cylinders which don't have full insulation. 4 pieces which tie on. Easy to do yourself and it does make a difference. https://www.screwfix.com/p/hot-water-cylinder-jacket-18-x-80mm-x-1219mm/43483. The recommended insulation thickness is 80mm. If you have an older tank you can check this by sticking a pin into the existing hard insulation.