R value is a measurement of resistance to temperature transfer. For example, a window with an R value of R2, will keep heat from passing in or out roughly 20% better than a window with an R value of R1.

Single glazed: This is a single piece of glass. It has very little R value at about R1, compared to double glazed glass with a value of about R3.

Double glazed: This is the most common modern type of glass found in almost all new windows and doors. It is two pieces of glass about half an inch apart and sealed around the outside edge. This "dead air" space between the glass reduces temperature loss directly through the glass itself. (Triple glazed glass would then be about R4).

Low E glass: Low emissivity film is a clear film applied to a single piece of glass that protects from heat loss directly through the glass and is about 20% more efficient than untreated glass. It can also reduce condensation on the interior of the window.

Argon gas: This is an inert gas witch replaces the air in a sealed glass unit to reduce convection heat loss. This can bring the R value up from R3 to over R4.

A double glazed window with Low E and argon gas can have a value over R9 or 80% over a clear single pane window.

In the summer, a single glazed clear window of 4x5 feet can add up to 8500BTU to your home due to the sun shining through it, which is equivalent to a 2500 watt space heater!

Plexiglass: Polycarbonate resin (Lexan) can be crystal clear or colored, textured or smooth. It can withstand up to +100 degrees C and as low as –40 degrees C, water, weather, UV rays and even flame. It is very often used in bullet and blast resistant applications and prison separations.

Georgian wire glass: This is a type of thick security glass with a very strong mesh of wire right in the glass. This glass will remain in place if it gets broken. It is generally less expensive than Lexan and is used in many of the same applications. It can be used in fire/smoke separation doors and fire-rated doors.

Tempered glass: This is glass that has been heat-treated to temper the glass. This process strengthens the glass up to ten times its original strength. Commonly found in commercial applications such as a store front where safety is often a factor. This glass will break into "pebble" sized pieces less likely to cause personal injury.

Laminated glass: Commonly found in automobile windshields. A plastic film is sandwiched between two pieces of tempered glass giving it even more strength but allowing the glass to remain in place when broken. Laminating can also block up to 97% of UV rays and reduce high frequency sound.

High security/safety film: This is an extremely strong yet very thin film that can be installed on existing glass surfaces to defend against destructive conditions such as weather, explosions or smash and grab burglaries by holding the glass in place. It is commonly used on jewelry display cases and display windows.