Coated with micronized silica particles which activate clotting when tubes are gently inverted. Clear as glass with equal or better performance. Molded to be virtually unbreakable, providing a better level of safety than glass. Tubes have an 18-month shelf life from the date of manufacture. Pediatric tubes come with white rings for quick identification. Safety Twist Caps can be removed and replaced several times. Non-screw caps can be removed and replaced as often as required.