Abstract: A portable heat generating device in which fuel vapor and an oxygen supply (e.g. air) are directed through channels contained within a thin, flexible and compliant elastomeric sheet of material. Elongated catalytic heat elements, placed strategically within the channels, spontaneously interact with the fuel-air stream liberating heat energy. Means and methods are defined that permit flameless catalytic combustion to be uniformly extended over the length of each heat element, lowering power density but maintaining the overall power generated, permitting the use of many types of low temperature materials like plastics, polymers, and elastomers in the construction of the heater. The heat generation process is started by pumping an air stream into a reservoir containing a fuel source (e.g. methanol) thereby saturating the air stream with fuel vapor.