Abstract: A heat transfer device comprising at least an aggregate of fibers or sheet of fibres (60) with internal passages and holes capable of capillary transport of liquids capable of capillary convection of coolant fluid from a heat source region (54) to heat dissipation region (56) and vice versa. A supply of coolant fluid in sufficient amount is provided to be absorbed or contained by said fibers or sheet of fibers (60) with internal passages and holes capable of capillary transport of liquids. A pressure tension member (70) comprising a strong yet resilient structure placed within said confined space and exerting pressure on said aggregate of fibers or sheet of fibers (60) with internal passages and holes capable of capillary transport of liquids against said heat source region (54) and/or heat dissipation region (57).