Laboratory Separating Funnel, This is the perfect filter flask for any chemist or lab tech. It holds 500 ml of liquid, which is enough for even the most ambitious experiments. The flask itself is made of high-quality borosilicate glass, which is strong and heat resistant. The lid is made of stainless steel, and the filter is made of durable filter paper. The filter flask is also very easy to use - just fill it with liquid, place the filter paper in the lid, and attach the lid to the flask. Then just place the flask on a heat source to filter out any unwanted substances.