The invincible grocery bags with the strength of paper and the ease of plastic. The invincible grocery bags with the strength of paper and the ease of plastic. Stronger and more durable Hippo Sak is made stronger, thanks to our innovative Power Strip and tri-flex film. The Power Strip creates a reinforced bottom seal, making Hippo Sak 10 times stronger than standard grocery bags. No more leaks, holes or tears. Reduces bag usage - it takes 3 to 4 of the standard non-reinforced bags to hold groceries that 1 Hippo Sak will fit. On average, Hippo Sak has increased items per bag by 25 percent and reduced bag usage by 20 percent. Environmentally friendly - made from U.S. polyethylene derived from natural gas, not crude oil.