IsoFreeze PCR racks are manufactured with a gel-filled center section that uses temperature-dependent color-change material, green to yellow or purple to pink. There is a dramatic change to a contrasting color at 7°C, so you can use this indicator to determine when the temperature of the rack, or even a single well, is rising to above standard refrigeration temperature. Each rack comes with an individual snap-on lid made of clear polypropylene. Comes in a package of 2.