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I think better than Popsicle bags ziplock gallon freezer bags would work best. I use them all the time for sprains they are reusable and they last a long time. Add a 1/4" of water to the bag when it's flat andstart the freezing process until its slushy, then add a paper towel to one side and roll around a wooded skewers. This creates a coil effect which allows for more surface area and solves the condensation problem.