AUTOCLAVE INDICATING - Labels change color from Green to Purple when exposed to autoclave temperatures. TOUGH - Chemically inert, polyester labels resist most organic solvents and caustic agents. TEMPERATURE-RESISTANT - From -40°C to 121°C, Tough-Tags resist boiling water baths and freezer temperatures. IDEALLY SIZED - Fits a variety of microcentrifuge tubes, microscope slides and other laboratory containers.