Glass Knowledge


Glass Weight per Square Foot:

  • 1/8″=1.64 lbs. sq.ft.
  • 3/16″=2.45 lbs. sq.ft.
  • 1/4″=3.27 lbs. sq.ft.
  • 3/8″=4.91 lbs. sq.ft.
  • 1/2″=6.54 lbs. sq.ft.
  • 3/4″=9.84 lbs. sq.ft.
  • 1″=13.11 lbs. sq.ft.

Formula for Figuring Linear Inches:

  • Rectangles: (width x 2) + (length x 2) = Linear Inches
  • Circles: Diameter x 3.2 = Linear Inches
  • Octagons: Diameter x 3.3 = Linear Inches
  • Hexagons: Diameter x 3.5 = Linear Inches
  • Ovals (width x 2) + (length x 2) = Linear Inches

Formula for Figuring Square Feet:

L” x W” divided by 144 = Square Feet

Example: 48″ x 96″ = 4608″
4608″ / 144 = 32 Sq.Ft.


– From the Greek word argons (inactive)
– Atomic Number: 18
– Atomic Mass: 39.948
– Thermal Conductance: 47.87% LOWER than air
– BTU over hour foot degree F: [(.0139-.0094)/.0094]
– Density: 38.01% MORE DENSE than air
– Pounds per cubic foot: [(.1111-.0805)/.0805]
– Viscosity: 22.16%MORE VISCOUS than air
– Pound seconds per square foot times ten to the negative fifth: [(.0441-.0361) /.0361]

Argon is about a 30% lower thermal conductivity than does air. This translates into about a 16% energy improvement in a standard LowE^2 IGU at better than 90% fill.

If you have an IGU with a 50% fill, for example, the U factor improvement will be 8% and at 75% fill the improvement will be 12%…you might note the straight line progression on u value improvement based on the amount of argon fill.

The air we breathe is 1% argon. If the IGU is filled to anything over that level, then the argon in the IGU wants to reach equilibrium with the 1% in the atmosphere. The job of the IGU manufacturer is to ensure that the argon in the IGU stays in the IGU. A 1% per year loss of argon due to natural dissipation thru the IGU edge seal (not resulting from a failed seal) is about the best that is currently available to modern technology. This is readily achievable and is becoming something of the industry standard.

Safety Glass

Safety glass is a type of glass that is designed to resist breaking, and to break in a way that minimizes the risk of injuries in the event that the glass cannot withstand the forces exerted on it. Car windows are classically made from this type of glass to promote safety in collisions, and it can also be used in regular house windows, eyeglasses, laboratory glassware, and a wide variety of other products. As its name would seem to imply, it is meant to be safer than ordinary glass.

There are two ways in which safety glass can work: tempering or laminating.

Laminated – A process by which two or more lites of glass are sandwiched about a polyvinyl layer to give the glass strength against penetration. It is not shatter proof or unbreakable. The most common application that everyone should be familiar with is automobile windshields.
Tempered – The process of heat-treating glass, to provide much stronger characteristics than annealed, or un-tempered glass. Once again, tempered glass is not shatter proof or unbreakable. It is designed to break into very small pieces to help alleviate severe lacerations. This process is used on automobile side and rear windows as well as storefronts and doors that are required by local building codes.


Uniform load strength – Heat-Strengthened Glass
Note: Data obtained from Fed. Spec. DD-G-1403.
The values have not been verified

Nominal Glass
Thickness. mm (in)
Average Breaking Pressure times Glass Area.
Pa x m2 (lbf x ft2).
Minimum value
3 (1/8) 5895 (1,325)
5 (3/16) 14,800 (3,325)
6 (1/4) 24,000 (5,400)
8 (5/16) 32,700 (7,350)
10 (3/8) 55,000 (12,000)
12 (1/2) 70,000 (16,000)


Window glass is by nature highly thermal emissive as indicated in the table above. To improve thermal efficiency (insulation properties) thin film coatings are applied to the raw soda-lime glass. There are two primary methods in use: Pyrolytic CVD and Magnetron Sputtering The first involves deposition of fluorinated tin oxide at high temperatures. Pyrolytic coatings are usually applied at the Float glass plant when the glass is manufactured. The second involves depositing thin silver layer(s) with antireflection layers. Magnetron sputtering uses large vacuum chambers with multiple deposition chambers depositing 5 to 10 or more layers in succession. Silver based films are environmentally unstable and must be enclosed in an Insulated glazing or Insulated Glass Unit (IGU) to maintain their properties over time. Specially designed coatings, are applied to one or more surfaces of insulated glass. These coatings reflect radiant infrared energy, thus tending to keep radiant heat on the same side of the glass from which it originated, while letting visible light pass. This results in more efficient windows because radiant heat originating from indoors in winter is reflected back inside, while infrared heat radiation from the sun during summer is reflected away, keeping it cooler inside.



Insulated glazing (IG), more commonly known as double glazing (or double-pane, and increasingly triple glazing/pane) are double or triple glass window panes separated by an air or other gas filled space to reduce heat transfer across a part of the building envelope.

Insulated Glass Units (IGUs) are manufactured with glass in range of thickness from 3 mm to 10 mm or more in special applications. Laminated or tempered glass may also be used as part of the construction. Most units are manufactured with the same thickness of glass used on both panes but special applications such as acoustic attenuation or security may require wide ranges of thicknesses to be incorporated in the same unit.

To reduce shear effects on the sealed unit (a major cause of premature failure), manufacturers use a rule of thumb that permits a difference of 1 mm between the Thickness of the panes of glass used in the unit and still maintain the warranty for the unit. For example, a unit may be ordered with a 4 mm pane on the exterior and a 3 mm pane on the interior. These variations are allowed for architectural and cost reasons. Other combinations can be specified and produced but the manufacturer may reserve the right to limit the term of the warranty or refuse to warranty the unit altogether.



Between each pane of glass in a window is a narrow space. This space is filled with a gas to provide additional temperature insulation. The most common gas used is air. Air provides decent insulation capabilities and is extremely cheap in relation to other glass window insulation gases.

Windows have come a long way in terms of technology and heat resistance. Most home windows these days are double- or triple- paned. This means that two or three sheets of glass are placed in succession of each other. This adds further hot and cold resistance from outside temperatures.

Argon gas is an increasingly common gas used in window insulation. The chief benefit of argon is that it is approximately five times heavier than air. This extra weight limits the total movement of the gas, which serves to further bolster window insulation. While more expensive than air-filled windows, argon gas windows have the potential to save homeowners a considerable amount on energy bills. Over time, these savings may result in a long-term reduction of costs.

Like air, argon is completely transparent. It also is odourless. This means that air-filled windows and argon-filled windows look exactly the same. It is also important to note that argon gas is nontoxic. As such, a cracked or broken argon window is just as harmless as an air-filled window (except for the shards of glass, of course).



Laminated glass is a type of safety glass that holds together when shattered. In the event of breaking, it is held in place by an interlayer, typically of polyvinyl butyral (PVB), between its two or more layers of glass. The interlayer keeps the layers of glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces. This produces a characteristic “spider web” cracking pattern when the impact is not enough to completely pierce the glass.

Laminated glass is normally used when there is a possibility of human impact or where the glass could fall if shattered. Skylight glazing and automobile windshields typically use laminated glass. In geographical areas requiring hurricane-resistant construction, laminated glass is often used in exterior storefronts, curtain walls and windows. The PVB interlayer also gives the glass a much higher sound isolation rating, due to the damping effect, and also blocks 99% of incoming UV radiation.