Microwavable Hot And Cold Gel Ice Pack Reusable For Pain Relief 2in1 HOT and COLD. Hot and cold therapy is a treatment that uses either heat or cold to relieve pain. Heat therapy dilates, or widens, blood vessels and increases blood flow to the area, which helps to reduce inflammation and pain. Can I apply ice pack directly? Ice pack or cold compress Fill it partially with water. Seal the bag, squeezing the air out of it. Wrap the bag in a damp towel and put it on the affected area. Do not apply ice directly to the skin. hot pack use As a general rule of thumb, use ice for acute injuries or pain, along with inflammation and swelling. Use heat for muscle pain or stiffness.