Pyrex Glass Test Tubes with Rubber Stoppers Set of 5 - Full Color Purple - Additional Vibrant Colors Available by TableTop King Heat Tempered Pyrex Glass. Includes Rubber Stoppers. These disposable PYREX glass round bottom test tubes. They are made of borosilicate glass to reduce pH changes and contaminants potentially. Due to variant temperatures from each manufacturer of dishwashers we recommend hand washing this product.