Wool

Hard mineral wool has better insulation and construction properties than soft wool. Because it cannot be "wound" onto the pipe, it is cut into wedge segments that are stacked around the pipe to essentially form a circle in a cross-section. It is laborious, but the fact that the hard mineral wool does not compress under the weight of the service pipe, guaranteeing constant thermal insulation properties for the lifetime of the pipe, compensates for this disadvantage.