Phillips multi-stoppers are manufactured of red silicone rubber and green neoprene. The rings are cut from the same stopper, each ring fitting perfectly inside the next. This allows for vacuum tight fit for all openings within stopper size range. Ideally suited for glass working operations and chemistry labs. Multi-stoppers made of red silicone rubber are suitable for higher temperature applications with a serviceable temperature range from -100F to +450F. These stoppers are resistant to hot oils, fuels, oxidizing chemicals, sodium hydroxide and ozone. Multi stoppers made from green neoprene rubber have better aging characteristics than those of natural (black) rubber and are resistant to oils, solvents, ozones and hydrocarbons. The serviceable temperature range is from -40 Degrees C to +100 Degrees C.