Generally, solids expand on heating. Glass is thus the preferred material to be used in ovens. But even among glassware, only a particular kind of glass is best suited to oven use. When normal glass heats up, the inner surface of the glass does not expand as much as the outer surface does, causing the glassware to develop cracks and eventually break. In the case of glassware like Borosil, the vessel has a thinner glass surface and the inner and outer surfaces expand equally ensuring its durability.