Acrylic vs. Glass: Providing Clarity on the Debate

Adjusting the corner of an Indow insert: winter scene visible through acrylic insert & glass window.

You’ve likely heard of plexiglass. What you may not know is that “plexiglass” is a word that came into being through the brand Plexiglas®. When a company dominates the market for a product, the brand name can become the name used for the product itself. The last time you had a paper cut, you probably walked to the medicine cabinet for a Band-Aid instead of a bandage. Plexiglas® is the brand that dominated the market for acrylic, a plastic material that is extremely difficult to break. Even when it does break, it does not shatter. Additionally, acrylic has a very high clarity. Hey, that sounds like it might be the ideal material for a window insert!

Now that we know what acrylic is, let’s talk about why Indow chose acrylic over glass for their interior storm window inserts. Performance and aesthetic were key in making this decision.

Thermal imaging of home window before and after Indow insert: plexiglass keeps in heat

Right window fitted with Indow insert, left window has no insert. The white thermal imaging of the left window indicates that heat is escaping through the window more quickly than the right window with its insert keeping heat in.


Acrylic and Heat Transfer

Do you mind chatting about science for a moment? We promise it will be quick and painless. Heat flows from warmer objects to colder objects. Imagine holding an ice cube. Because heat moves from warmer objects to colder ones, heat moves from your hand to the ice cube, causing it to melt. If heat moved from colder objects to warmer ones, then your hand would warm up while holding ice and the ice would remain intact.

Glass does not retain heat well. In the winter, your warm inside air meets your glass window and because heat moves from warm objects to cold ones, the heat moves through the glass and into the cold outside air. You have to run your heat continuously in winter because heat is escaping from the warm inside to the cold outside. The great news is that acrylic retains heat well. Because we use acrylic, Indow inserts transmit heat seven times more slowly than regular glass. As a result, heat moves from the insert and through the window frame to the cold outside air much more slowly. Warm inside air moving out more slowly means you don’t have to run your heating system as much to maintain your desired temperature. In turn, you save on energy bills. This is a benefit in summer as well. Since Indow inserts retain heat well, the hot outside air penetrates into your home much more slowly, so you don’t need to run your AC as much to maintain your desired temperature.

Case Study House #26: acrylic Indow inserts help block draft through the large glass windows

Aesthetic and Usability

Another reason why we chose acrylic over any type of glass insert is because of the weight and clarity. The weight of ⅛’’-thick glass is 1.62 pounds per square foot. The weight of ⅛’’-thick acrylic is 1 pound per square foot. A 3×4’ Indow insert will weigh 12 pounds, while a 3×4’ glass insert will weigh around 19.44. 3×4’ is considered an average window, but you may have larger windows. Using the lighter acrylic for our inserts allows for much easier handling during installation and removal. Additionally, acrylic can withstand high impact and pressure. On the off chance that it breaks, it won’t shatter into sharp shards like glass does. That’s why it’s used on submarines and airplanes.

It might come as a surprise to hear that glass has a visible light transmittance score of less than 100%. However, if you think about driving in a car with a clean window that’s rolled up, you have great visibility through the window, but if you roll it down the picture outside of the window is even clearer. It might also come as a surprise that acrylic has a higher visible light transmittance than glass. A single-pane window has a transmittance of 90%, while a Standard Grade Indow insert is 92%. Yet another reason Indow chose acrylic for our inserts: we want you to feel results without seeing the technology behind them.

Window fitted with Indow insert next to window with no insert & significant condensation buildup

Acrylic and Condensation

Let’s talk about condensation and if glass or acrylic is better at combating it. To do so, we’re going to have to get a bit scientific again. Ready? The dew point is the temperature at which air cannot hold any more moisture. And that temperature is lower than the air temperature. When air hits a cold surface, its temperature drops. When the air reaches its dew point, water will form on the cold surface. We already learned that glass does not retain heat well, so when it’s cold outside, the glass is also cold. When the outside temperature cools the glass to the dew point of the inside air, condensation will form on the window when the inside air meets the glass. Indow inserts are great at reducing or eliminating condensation because it retains heat so well. The cold air will not be able to cool the acrylic to the indoor air’s dew point. For a less condensed explanation of this issue and how acrylic can eliminate it, read more here about removing window condensation.

Man installing Indow insert behind blinds in his bay window

Other Factors to Consider

Indow does not recommend our inserts as a window replacement product. They should always supplement an existing window. This is because, when compared 1:1, acrylic is not necessarily better than glass for noise reduction and scratch resistance. Indow inserts are designed to be a secondary window product, never a primary.

To address noise issues, Indow created the Acoustic Grade insert. It is the thickest insert offered at ¼’’ and reduces noise coming through your window opening by 50-70%*. When your Indow representative considers solutions to your noise issues, they want to know how much space you are able to put between your window and your insert, the type of noise that is bothering you, and the distance from the source of the noise. The bigger the air gap between the window and insert you can create, the better noise reduction you are going to observe.

5-star review of Indow inserts’ ability to block street noise with acrylic panels

The Commercial Grade insert comes with an additional one-sided or two-sided film that makes it more abrasion resistant. It performs better than anti-scratch window film, making it an appropriate solution for sports facilities and other highly trafficked areas in which they might be bumped much more than in your home. While the Commercial Grade is available to all Indow clients, including those with residential projects, the additional abrasion-resistant film is not absolutely necessary if you plan to keep your inserts in place and you do not have children or pets running out. For those who do have energetic children and lively pets, the Commercial Grade is a great solution.

Much thought and consideration went into the decision to use acrylic panels over glass. It was absolutely the right decision. As a result, Indow is able to offer a product that reduces heat loss, condensation, and noise and is easy and safe to handle. And because acrylic is cheaper than glass, we are able to offer it at a fraction of the cost of expensive window replacements. Take a look at all product types to learn about other issues Indow inserts can help you address. 

Indow is proud to work with local recyclers within Portland for our leftover acrylic materials. We also donate materials to Scrap. Scrap upcycles already manufactured materials for artistic purposes and to create new use for these existing items.

*We want to ensure our inserts help solve your noise problem. Overall noise reduction depends on the amount of noise coming through your walls, ceilings, floors, doors, and existing windows. Noise reduction will be less when placed over double-pane windows. Read our full Noise Reduction Sheet to learn more.