Patent ID: 7878187

Claim:
A heat cell comprising a particulate exothermic composition wherein the particulate exothermic composition comprises: (a) from about 10% to about 90% by weight of iron powder having a median particle size of from about 50 μm to about 400 μm; (b) from about 1% to about 25% by weight of a carbon selected from the group consisting of activated carbon, non-activated carbon, and mixtures thereof; (c) from about 1% to about 25% by weight of an absorbent gelling material having a median particle size of from about 300 μm to about 800 μm; and (d) from about 1% to about 35% by weight of water; wherein the particulate exothermic composition comprises a median particle size ratio range of absorbent gelling material to iron powder of less than 3:1 to 1:3; wherein the particles of the particulate exothermic composition are combined in a pocket, formed in a unified structure comprising at least two opposed surfaces, wherein at least one surface is oxygen permeable; and wherein the particulate exothermic composition in the pocket has interstitial particle void volume.