Abstract: Apparatus for and method of manufacturing a heat insulating material from an uncured, strip-shaped felt of fibres containing a heat hardenable bonding substance firstly form corrugations extending across the entire width of the uncured felt and following one another in succession along the length of the felt. The corrugated felt is then cured as a cured felt containing fibres extending in a serpentine array along the felt, and conveyed along a path of travel extending past a cutter having a cutting blade extending transversely across the path, whereby the felt is cut longitudinally into two partial felts, the corrugations being severed so that the fibres form U-shaped arrays disposed in succession along each of the partial felts. This fibre array provides compressive strength combined with flexibility, enabling the insulating material to be used on various pipe sizes.