Rice Bag Therapy is about healing. These handmade rice bags are perfect for soothing sore muscles, cramps, migraines, fevers and chills. For Heat Therapy: Place a mug of water in the microwave beside your rice bag and heat for 1-2 minutes for warm (2-3 minutes for hot). This may vary by microwave. For Cold Therapy: Place your rice bag in the freezer for 2-3 hours for best results.