Laboratories and other stringent environments can count on the purity of these binder-free filter sheets, which have been conditioned by high temperature preheating. Grade MK 5 sheet is suitable for air monitoring applications in high temperatures, aggressive atmospheres and when low levels of trace elements are essential. Grade MK 360 sheet featuring 100% quartz microfibers is for applications with even higher temperatures (500 to 900°C) demanding extremely low levels of trace elements.