Buchner filter funnels have a jacket that covers the entire funnel bowl as well as the upper section of the stem. During filtering, liquid circulation through the jacket allows the funnel and contents to be warmed or cooled. They come in coarse (C), and medium (M), porosities and are made of borosilicate glass with a sealed-in fritted glass disc. The length of the stem listed is the length of the stem below the jacket.