Flat Bottom Flask,2000M?L,24/40,3 neck,Three Neck,Chemi?stry Lab Glassware 1 Be made of G3.3 borosilicate glass. This borosilicate glass with low linear coefficient of expansion is ideal choice for fabricating laboratory glassware. Annealing Point ------560 Degree C Linear Coefficient of Expansion ------ 32×10-7/ Degree C Softening Point ------820 Degree C 2 The thickness of the flask is 2.5mm.