DURAN® Kjeldahl flasks are subjected to extreme chemical and physical stresses. Therefore, the wall thickness should not be too thick to avoid overheating, which can lead to breakage due to remaining (permanent) stresses, on the one hand, and not too thin due to the noticeable glass removal in the alkaline medium, on the other hand. In order to offer the user the safest possible compromise while taking the technological conditions into account, the wall thickness of the DURAN® Kjeldahl flasks in the body are 1-2 mm.