What is Window Desiccant?

What is Window Desiccant?

Simply defined, window desiccant is absorbent material installed between the panes of multi-paned windows to absorb excess moisture and prevent condensation. However, when you look a little deeper, you will see that window desiccant is a little more complex than that, and the causes and cures for window condensation are as well. Read on to learn more.

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What causes window condensation?

Essentially all air contains moisture in certain and fairly predictable amounts. When air is warm, the molecules of moisture are far apart and remain suspended in the air. When the air cools, they get closer together until they reach a temperature known as a dew point.

The dew point varies↗ depending on humidity, temperature, and pressure. For simplicity, when the air between the window panes contains enough moisture and reaches this dew point, condensation forms. So what does window desiccant have to do with it?

What is window desiccant and how does it prevent condensation?

Window desiccant is a super absorbent material that removes moisture from the air. Generally, window desiccant has a lot of surface area and will last a long time before becoming saturated.

Double-paned windows go through a daily process of thermal exchange, flexing, and moving against the seal that keeps an inert gas inside to promote insulation and the elements outside. The window desiccant is designed to absorb any moisture that enters the air between the panes during this process.

Types of window desiccant

There are a few different types of window desiccant made up of different materials. They all work a little differently and last varying lengths of time depending on what they are made of.

  • Clay: This desiccant is made up of a special type of clay and is then broken into beads. It is effective as long as the area it is used in does not experience extreme temperature swings even if it is relatively humid. Temperatures over 120 degrees will cause performance to degrade.
  • Silica Gel: This is one of the most common desiccants, due in part to its high surface area that allows for the absorption of a lot of moisture and its stability in a variety of environments.
  • Molecular Sieve: The very best desiccant for rapid absorption and stability is a molecular sieve, which is made of aluminosilicate. It’s stable, absorbs a lot of moisture quickly, and works especially well in areas with high relative humidity. While extremely effective, this is also the most expensive desiccant option.

Silica gel or silicone insulation strips with a desiccant integrated into them are very common in double-paned windows.

Features & Benefits of Quality Desiccant

Why is silica gel so common? Another part of the equation in windows is the desiccant compatibility with the insulating gases. The best desiccant to use depends on not only the gas used but the relative humidity and average climate of the geographic area where the window will be installed.

Ideally, a high-quality desiccant will have:

  • High water absorption capacity: This is especially important over time. Typically, the length of a window warranty may be based in part on the desiccant used.
  • Low dew points: The lower the point of condensation, the less likely it is to form.
  • Compatible with insulating gases: as already stated, some desiccants can be compromised by the insulating gas in the window, so both need to work well together.
  • Extends the life of the insulated glass unit: The desiccant that can absorb moisture over time with a low dew point will increase the life of the window unit by decreasing condensation and window failure.

The better the desiccant, the longer the life of the window. But there can be other mitigating factors that degrade desiccant effectiveness and can cause it to fail.

Desiccant Strip Failure

Why would a desiccant strip fail? The short answer is this is caused when the moisture between the window panes exceeds the amount the desiccant can absorb. The cause is a bit more complex.

Windows flex and move with temperature changes, and eventually, even the best window seals will develop cracks, dry out, and then allow air, and therefore moisture to enter the space between the two window panes. The gas that helps insulate the window will often leak out when this happens as well.

When the desiccant becomes over-saturated, you will see condensation between the window panes. What this really means is that the window unit itself has failed and is no longer doing a good job of insulating your home.

Recommendations for failed windows

There are only a couple of solutions for failed windows. You can take temporary measures, where a company will come out, attempt to reseal the windows, and then will re-inject the inert gas between the panes after using a device to “dry” the inside of the windowpane and remove moisture. This usually only works for a limited time because it requires drilling a small hole and resealing it after the gas is inserted. It won’t remove all the moisture from the desiccant, meaning this “repair” won’t last long before it becomes overwhelmed again.

The ideal solution is window unit replacement. You start with new seals, new desiccant, and the assurance that the window is again insulating your home effectively. There are some exceptions to this, and the best way to determine the right solution for you is to call a window or glass professional for a consultation.

The desiccant between your double pane windows is designed to help preserve the life of your window by removing moisture from the air. There are several types, and your window installer can help you choose what is right for you and your home. Once it stops working, you’ll need to determine why, and what your options are going forward.


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