The invention relates substantially to brush consisting of a number of wire bundles forming knots and extending radially from the periphery of a heat conducting disc supporting the wire bundles, all being covered by a first layer of elastomer which has attached to it a second layer of elastomer of substantially less diameter, extending over a portion of said knots; the remainder of the knobs being left uncovered by the second layer thereby forming a flexible base for the movement of the knots as well as permitting heat conduction to the air.