This invention concerns a mechanical friction device (10), in particular a brake or clutch disc. The friction device (10) includes a central layer (16) which is sandwiched between two outer, friction layers (18.1, 18.2). The central layer (16) has a porosity level higher than that of the two friction layers (18.1, 18.2). The central layer (16) is in the form of a wire-frame structure (30, 40) which acts as heat transfer means to transfer heat away from the friction surfaces of the outer, friction layers (18.1, 18.2). In the preferred embodiment the wire-frame structure is either an X-type lattice sandwich structure (30) or a wire-woven bulk diamond structure (40). This invention also concerns the use of wire-frame structure as a heat transfer means in a mechanical friction device (10) such as a brake or clutch disc.