Vacuum glass is to seal the two sheets of flat glass, leaving a gap in the middle, vacuuming the gap and sealing the vent. The inner surface of the two sheets of glass is coated with one or two transparent low-emission films. The hollow glass is called "hollow" and is not empty. There is "qi" in the middle of the two layers of glass. In most cases, "qi" is air, and the better quality is argon. Since the gas is not visible to the naked eye, it is said to be "empty. Empty glass is to draw a "vacuum" between the two layers of glass, basically it can be said that there is no gas, it is really empty.