Insulated Glass Benefits and Types: What You Should Know

Insulated glass, also known as IGU, can regulate temperatures and improve your window’s energy efficiency.

If you’re getting ready to purchase new windows, it’s important to keep energy efficiency in mind. Windows can be a significant source of heat loss in the winter and cool air in the summer. Choosing the correct type of glass can prevent this.

Insulated Glass

One option that’s almost always worth the cost is insulated glass. If you’re unfamiliar, here are the types and what you should know about each.

What is Insulated Glass?

Insulated glass has two or more panes. There’s a gap between panes created by a spacer. Then, manufacturers fill the space with air or dense gas that acts as an insulator.

Insulated glass goes by many names, including double-pane, double-glazing, triple-pane, and triple-glazing. These windows are a “unit” because they contain many parts rather than one piece of glass.

And because insulated glass units are filled with gas and sealed, you can’t replace just one piece of glass or make repairs.

Types of Insulated Glass

All insulated glass has similar components- two or more panes of glass, sealed, separated, and filled with an insulator.

The difference between the types is what fills the space between the panes. 

  • Air-filled– As the name implies, air-filled glass has air between the glass panels. Air provides increased energy efficiency, but not as much as gas-filled options. The benefit is the seals last longer than on gas-filled units. Air-filled insulation is also the least expensive.
  • Argon insulated glass – Argon is a dense gas and the most popular window-insulation option. Argon-insulated windows can increase energy efficiency by about 10% compared to air-filled units. Many argon-filled windows also have Low-E coatings to prevent heat leaks.
  • Krypton insulated glass – Krypton gas is denser than argon and popular in windows with small gaps between the panes. Krypton is an excellent insulator but comes at a higher price.
  • Xenon insulated glass– Xenon is a dense, expensive gas. It’s most popular in commercial architecture, where there are large spans of windows. Xenon might not be worth the cost in residential spaces.

Is Low-E Insulated Glass?

Low-e glass is a microscopic coating, not an insulator. Low-e stands for low emissivity – it reflects heat off a window and back inside the home. A type of  Low-E glass, called solar-control low-E, can also prevent most solar heat from entering the windows.

For maximum energy efficiency, choose a window that’s insulated (double or triple-paned) and has a Low-E coating.

Can You Repair an IGU?

One of the downsides to insulated or thermal windows is that you can’t replace pieces. If the seal weakens on your window or a portion of glass gets damaged, you’ll need to replace the entire unit. But that doesn’t mean you have to replace the whole window – instead, you can replace the damaged sash.

What are the Pros and Cons of Insulated Glass?

If you’re considering insulated glass for your next set of windows, the energy efficiency is almost always worth it. 


  • Improved energy efficiency – Heat can easily escape the glass. The insulation of IGU helps prevent this.
  • Noise reduction – The double or triple panes of glass can act as a sound barrier reducing noise transfer from outside.
  • Safety – Glazed glass is considered safer from burglary.
  • Easy to find – Insulated glass is the standard, easy to find from all top manufacturers.


  • Hard to repair – You must replace entire sashes or insulated glass rather than repair it.
  • Can fog if seal breaks – A faulty or old seal can lead to fogging between the window panes.
  • More expensive – Gas-filled insulated windows are more expensive than air-filled or single-pane windows.

How Much is Insulated Glass?

Insulated glass is about $3-$20 per square foot, depending on the type of insulator and how many panes a window has. A double-glazed, air-filled window will be the least expensive, while gas-filled and triple panes will increase the price.

Frequently Asked Questions (FAQ)FAQ

Can you replace just the glass in a double-paned window?

Double-pane windows have a tight seal, with a spacer and sometimes a gas filling between the panes. The tight seal is one of the reasons these windows are so energy efficient. So, you cannot replace just a piece of glass in a double-paned window because it won’t have a tight seal. Instead, you’ll need to replace the entire sash or unit.

Can you refill the space in double or triple-paned glass?

No, the entire glass unit needs replacing when something goes wrong with a double or triple-pane window. 

What’s the best type of gas for glass insulation?

Xenon is the most insulative gas for glass insulation but may not be worth the price. Krypton and argon are also good options, with krypton being denser but more expensive.

Is thermal glass different from insulated glass?

No, thermal glass is the same as insulated glass. Both feature two to three panes of glass with space in between that manufacturers fill with air or gas to increase a window’s energy efficiency.

Are glass block windows insulated?

Glass block windows have more than one pane of glass and offer similar energy efficiency as double-glazed windows. If you’re in the market for new windows, you can look for the Energy Star logo to find insulative glass block windows.

Final Thoughts

Insulated glass has many names, including IGU, double-pane, double-glazing, and triple glazing. These windows feature two or more panes of glass, separated by a spacer and filled with air or gas to insulate.

The most popular insulated glass window has an argon gas filling. While krypton and xenon gas are denser, they’re more expensive and not always worth the higher cost. Look for an insulated window with a Low-E coating for maximum energy efficiency.