As a type of superabsorbent polymers, sodium polyacrylate can absorb plenty of water and become a gel form.
One-gram sodium polyacrylate can absorb 300-1000 grams of pure water. In other words, it's enough to contain 1 gram (or less) sodium polyacrylate for each gel ice pack.
Advantages of Sodium polyacrylate
high specific heat capacity;
low cost (for each gel ice pack) ;
non-toxic & environment friendly;
Other applications of sodium polyacrylate
Except for gel ice pack, it can be used in every aspect of our life:
thermal insulation material (ice towels, ice pillows...);
absorbent material (such as in paper diapers, sanitary napkins, nursing pads...);
water blocking material (such as inflatable sandbags, waterproof for cable...);