TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The thermal barrier comprises an envelope comprising a hydrophobic material containing the hydrogel. The hydrophobic material is a foil pouch. The foil pouch contains a supporting structure comprising a porous sponge material. The supporting structure comprises many independent cells each containing the hydrogel. The supporting structure comprises a natural cotton material. The thermal barrier: has a first normal state, a second hot state and a third vented state; comprises a thermal absorbing material comprising 99% water; is disposed between the electrochemical cells in a battery and the battery housing (702); freely transmits thermal energy below an atmospheric boiling temperature; resists the transmission of thermal energy above an atmospheric boiling temperature; and includes a void for expansion and contraction of the thermal absorbing material contained in it. In the system: when in the hot state the thermal absorbing material exceeds its atmospheric boiling point and evaporates, thus increasing the size of the void; and when in the third vented state the thermal barrier envelope is breached for pressure release. The thermal barrier envelope includes a weak area to promote breaching when pressure within the thermal barrier envelope exceeds a predetermined pressure.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The thermal barrier comprises a hydrophilic polymer. The hydrophilic polymer is polymers comprising acrylics and amine-functional polymers. The acrylics comprise at least acrylic acid, acrylamide or maleic anhydride polymers and co-polymers. The amine-functional polymers comprise at least allylamine, ethyleneimine or oxazoline. The hydrophilic polymer is one of a sodium polyacrylate or a polyacrylamide-co-acrylic acid. The hydrophilic polymer comprises a hydrogel. The thermal absorbing material is doped with a dopant to vary the atmospheric boiling point. The dopant is a co-acrylic. The thermal absorbing material is present at 0.07 g/g of battery material.