What is the difference between online Low-E glass and offline Low-E glass?

Low-E glass( Low Emissivity Glass) is a coated glass with excellent heat insulation and energy saving. It also has high visible light transmittance. As a result, it can effectively reduce the external dissipation of indoor heat in winter. And in summer,  it can also block the secondary radiation of outdoor objects after the sun’s heat.

Low-E glass

What’s an online Low-E glass and offline Low-E glass?

According to the production technology, Low-E glass can be divided into “online Low-E glass” and “offline Low-E glass.” Online Low-E means that the glass coating is completed on the float line at one time. Off-line Low-E implies that the glass leaves the float line and goes to another place to finish the layer. See below for details of this two technology:

  • Online Low-E is a functional film with low radiation properties formed on the surface of the glass ribbon on the float glass production line through equipment modification, the chemical vapor deposition process, and unique materials.
  • Offline Low-E generally adopts a vacuum magnetron sputtering coating process to coat a multi-layer composite film on the glass surface to realize Low-E function. In the film layer, the main functional film layer is generally silver (Ag) film, and the other film layers are auxiliary films, which can strengthen the connection and protect the main film. According to the difference of Ag film, it can be subdivided into several different product categories such as single Ag, double Ag, and single Ag modified type. In addition, there are colorful colors for selection.

What’s the difference between these two technology?

  • Processability: The online Low-E glass film layer is hard, with good firmness and wear resistance. It can be stored, processed, cut as ordinary glass, and tempered and bent. It is usually used as a single piece or laminated, insulated glass. Offline Low-E glass, some films are soft, and the wear resistance and firmness are not very good. It is also sensitive to humidity, short storage periods, and high production costs. Some offline membranes cannot be used singly when exposed to air. It must be processed into composite products such as insulated and laminated.
  • Glass color and reflectivity control: The reflective color of the glass is the color of the exterior of the building that we see when the entire building is completed. There is only one variety of online Low-E, and the reflection color can only be changed by selecting different coated substrate glasses (clear glass, green glass, gray glass, blue glass, etc.). But, offline Low-E can change the variety of coated substrates, and the reflective color can also be flexibly adjusted through the choice of film material and structure.
  • Optional specifications: The offline Low-E glass can use any thickness of float glass. But the price will be higher if it is more than 15mm in thickness. But the thickness of online Low-E glass is generally only 4, 5, and 6,8,10 mm.
  • Cost: According to the experimental calculation results, using offline Low-E glass saves an average of 8% more costly than using online Low-E glass under normal circumstances.