Phase change materials could be a game-changer for energy storage. They absorb (and release) coldness when they freeze (and melt). They can earn double digit IRRs unlocking c20% efficiency gains in freezers and refrigerators, which make up 9% of US electricity. This is superior to batteries which add costs and incur 8-30% efficiency losses. We review 5,800 patents and identify early-stage companies geared to the theme in our new 14-page note.