A self-heating warming blanket includes a pliable outer shell forming a liquid impermeable enclosure. A heat generation layer disposed inside the enclosure has a plurality of liquid permeable heater compartments containing an exothermic reactant. The blanket also has a heater activation system including a sealed bladder containing an activator liquid inside the enclosure. An activation strip extends from outside the outer shell into the enclosure. One segment of the strip is an unsealing segment connected to the bladder. Another segment of the strip is a handle segment outside the outer shell. Pulling on the handle segment opens the bladder and releases the activator liquid into the enclosure where at least a portion of it permeates at least one heater compartment and combines with the exothermic reactant contained therein to initiate an exothermic chemical reaction that heats the warming blanket.