Regular ice is coldest, but hardest to re-use for muscle aches. The flexible ice-substitutes I've tried stink and melt too damn quickly. I suggest: wrap real water with thin, strong, flexible silicone. Make it 3D hexagonal, or pentagonal like 3d honeycomb shapes. When frozen, the little guys will be able to move into place in a flexible sheet ideal for icing your aches and pains. The silicone will keep the stuff in shape but be flexible while cold. Put the shapes in a sturdy but flexible bag (maybe more silicone), and tuck that (after frozen) into a velcro-riffic back brace wrap. Blammo!
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