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Glass Types

Float Glass

is produced by melting sand, soda-ash, limestone and dolomite in a furnace, and sometimes also mixing in recycled glass. The furnace outputs a continuous ribbon of molten glass that is floated onto a large bed of molten tin. This mixture slowly solidifies to a thickness controlled by the speed it is drawn over the molten tin. It is then annealed – control cooled – to ensure flatness.

Clear Float Glass

is transparent and colourless, offering high visible light transmittance and optical clarity. It offers little resistance to solar heat gain and glare in buildings.

Laminated Glass

is safety glass that has been manufactured by adhering two or more sheets of glass with a flexible interlayer. This interlayer, usually 0.38mm thick and manufactured from poly vinyl butyral (PVB), prevents the glass from disintegrating when broken.

Toughened Glass

is produced by passing cut-to-size annealed float glass through a heat furnace. This process introduces stress into the glass and produces a glass 4-5 times stronger than ordinary float glass. Toughened glass can still be broken, however if this does happen it shatters into small fragments, minimising the risk of injury caused by glass splinters.

Insulating Glass Units

(also referred to as double glazed units) consist of two panes of glass separated by a spacer around the edges and sealed to the perimeter in factory controlled conditions. The spacer contains a desiccant which eliminates moisture vapour in the cavity. Insulating glass units are available in many glass combinations, and the air gap between the glass panes can be filled with a range of gases

Low emissivity (Low-E) Glass

Low-E glass has a low rate of emission that is it has a lower rate than clear float glass of allowing heat to pass through the glass. In other words, if there is a heat source inside your house (or outside), the glass bounces the heat from that object back away from the glass. So, in the winter months, if you have Low-E glass in your home, much of the warmth (heat) given off by air conditioners, heaters and all the objects which they have heated, is bounced back into the room. In the summer, the same thing happens but in reverse. The sun heats things up (the air, sidewalks, driveways, next door neighbours bricks, etc.) outside of your house. This heat radiates from those objects and tries to get into your house. With Low-E glass much of this heat bounces off the glass and stays outside.

There are two types of Low-E glass: online coated Low-E (hard coat) and offline coated Low -E (soft coat). As you might imagine, they have different properties. In fact, they actually look different.

Online coated Low-E glass (hard coat)

is manufactured by pouring a thin layer of metallic oxide onto a sheet of glass while the glass is still on the float line, just after it has been formed into a thickness ribbon. The metallic oxide layer actually becomes “welded” to the glass surface. This process makes it very difficult or “hard” to scratch or remove the coating — therefore why it is referred to as “hard coat”. Often this glass has a bluish tint to it.

Offline coated Low-E glass (soft coat)

involves the application of silver, zinc or tin (or a combination of) to glass that has already been formed and taken off the float line. The glass enters a vacuum chamber filled with an inert gas which is electrically charged. The electricity combined with the vacuum allows molecules of metal to sputter onto the glass. The coating is “softer” than online coated glass — therefore why it is referred to as “soft coat”. Furthermore, if silver is used (and it often is) the offline coating can oxidise if exposed to normal air. For this reason, offline coated Low-E glass must be used in an insulated glass unit (IGU). Sealing the coating in between two pieces of glass protects it from outside air and sources of abrasion. Also, the space between the two pieces of glass is often filled with argon gas. The argon gas inhibits oxidation of the metallic coating. It also acts as an additional insulator.

Online coated Low-E glass (hard coat)

Advantages The coating is relatively durable, which allows for ease of handling. Can be used in single glazed applications. Utilises passive solar heat gain. Disadvantages Higher U-values compared to offline coated Low-E glass. Slightly higher haze levels. Higher solar heat gain coefficient compared to offline coated Low-E glass. Offline coated Low-E glass (soft coat)b Advantages High visible light transmission. Ultra-low emissivities giving optimum winter U-values. Up to 70% less UV transmission compared with standard clear glazing. Optical clarity — minimal colour haze. Disadvantages Must be used in an insulated glass unit. There can be slight colour variations of coating.