vince,
Not sure if this helps or not, but something I found out on the www.
Brian
Reusable ice packs contain primarily water, but additives are necessary to lower the freezing point of the water and to thicken the pack to reduce leakage. Coloring agents-usually blue-convey a "cold" image, while a preservative prevents bacteria and mold growth.
METHOCEL* cellulose ether is used as a thickener in reusable cold packs, as well as in a variety of products from shampoos to foods. METHOCEL is produced by the reaction of cellulose (obtained from wood or cotton) with methyl chloride, yielding methylcellulose. If propylene oxide is added to the reaction mixture, hydroxypropyl methylcellulose is produced. The number of substituent groups on the ring determines the properties of the various products.