This woven cloth filter is a special mixture of fibreglass and nylon. It is heat resistant and flameproof. This Protectaglass filter is 305mm size made to fit exclusively onto Numatic 305mm diameter metal-bodied vacuum extractors. It is the first line of filtration preventing hot particles reaching the main filter and motor when extracting from a grinder or boiler cleaning. Please note the vacuum extractor should also be fitted with a suitable heat resistant hose.-bg