A heat exchanger in which the main component is formed of a plurality of elongated strips of rigid heat conductive material. Each of the strips has a cross-sectional configuration which is elongated in a direction transverse to the elongated extent of the strip so as to provide a pair of spaced relatively thin end edges and a pair of relatively wide opposed surfaces extending between the end edges. The strips are generally transversely aligned and wound into a coil formation in which each of the surfaces of each strip is disposed in facing relation to the opposite surface of an adjacent strip in the coil. Each pair of facing surfaces is ridged to provide defining portions and force transmitting portions with certain of the strips having both end edges thereof sealingly secured to the corresponding end edges of an adjacent strip so as to define with the passage defining portions of the facing surfaces associated therewith a longitudinal fluid passage having a flow direction extending generally in the direction of longitudinal extent of the strips and with certain of the strips having both end edges thereof disposed out of sealing engagement with corresponding end edges of the adjacent strip so as to define with the passage defining portions of the facing surfaces associated therewith transverse fluid passage means having a flow direction extending generally in a direction transverse to the direction of longitudinal extent of the strips. The force transmitting portions of each pair of facing surfaces are disposed in force transmitting relation with respect to one another in the direction the facing surfaces face one another so that forces created by the fluid pressure and temperature conditions within the fluid passages tending to deform the strips in the facing directions are resisted to thereby prevent deformation which would otherwise occur in the absence of the force transmitting relationship and permit the utilization of wall thicknesses less than that required to be self-sustaining in order to prevent such deformation.