Why We Use Acrylic vs. Glass

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.

Nathan V

They are great. We live next to a busy street, so noise abatement was our primary interest. They have signicantly reduced street noise, and we'd definitely recommend these to anyone.

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.

Customer Reviews


4.49 Average 1477 Reviews logo

Matthew L

Indow inserts were easy to measure, order and install. They've provided great insulation for old single-pane and stained glass windows in an antique home. We can significantly feel how much better the home holds heat.

Posted 2 days ago

Ellis W

I ordered two Indow inserts for my home. They are doing a great job, entirely happy with them and the ordering process.

Posted 1 week ago

Elizabeth W

I can't say enough good things about this product and company. Our house is 101 years old and the sidelites next to our front door are single pane ancient wavy glass which means when it gets very cold (Chicago temps) we can have an inch of frost covering the INSIDE of our windows. I was desperately searching for a solution so our front vestibule was not so cold and a friend recommended Indow. The process could not have been simpler and the temperature difference it has made is off the charts.

Posted 2 weeks ago

Austin T

I have several historic single pane gridwork mullion windows. They're beautiful but have almost no thermal protection. Indows proved to be the perfect solution to preserve these windows while getting the thermal comfort we need. They were easy to install and work perfectly!

Posted 3 weeks ago

Kathryn M

Amazingly easy to install even the safety chain holders. I. Noticed an immediate sound level difference and the room atmosphere became more solid feeling and pleasant. They also gave an insulating feature to the window drafts are non existent! The house is 50ft off a State highway that is heavily traveled in warmer months I'm confident the indows will handle it. I'm very pleased!

Posted 1 month ago


We ordered the acoustic inserts to help with road noise, and we've been sleeping so much better with them!

Posted 1 month ago

Sienna K

We used the windows inserts in our skylight. They are great! They the horrible drafts and noise out and were cost efficient. My only comment would be to provide better measurement and installation instructions for skylights specifically. It took us a lot of guessing and research to measure and install because skylight directions were not provided and the windows install guide doesn't always apply to skylights. Other than that though great product and I would buy again!

Posted 1 month ago

ted t

Our home was built in the late 1800s and we have spent a lot of money over the last 20+years restoring it.We did not want to replace the windows with modern windows because of the cost and originality. But the single pane windows come with a price also. the main reason we purchased the Indow window inserts is because of the condensation on the inside of the windows.We would literally have a take a towel and wipe them down every morning in the winter. There would be a puddle on the sill,and wood and water dont get along to well. SO we looked into the best solution to our problem and found Indow. Was reluctant to spend that much money but am super glad we did!! They have been installed now for over two months and our condensation problem has been virtually eliminated.!!! AND our furnace does not run as much as it did before. Over all it was money well spent!! The process was a little scary at first but they have a simple formula. And our contact person,Reed was awesome. Answered any questions i had and was always available.

Posted 1 month ago


Used to block interior side of a garden window in the the kitchen. Without insert, cold air literally poured into the kitchen making a winter jacket almost mandatory when preparing meals or washing dishes

Posted 1 month ago

Rob S

Highly recommend! The team (Brian) took time to help me figure out the best solution. They were made and delivered faster than expected. It was very rewarding to install them because I could feel the cold air get squeezed out as they went flush against the single pane of glass. Solid quality and great fit.

Posted 1 month ago

Alexa L

My inserts fit beautifully into my 125 year old windows - many of which were 5 feet tall. Easy to unwrap and install. Great product and even better service! I liked the process of measuring the windows with a laser measuring tool which was easy to use and precise. The product came in good condition after shipping across country and was well marked. The customer support was excellent.

Posted 1 month ago

Sarah D

Received our Indow Windows and can tell they are blocking a lot of the noise we could hear. Right now the weather is mild, but hoping to notice a big difference when the summer heats up. Our house is in a historic district and we cannot change our windows. They are very drafty and thin glass. We only ordered two, but we are in the process of ordering for four more. Love that we don’t need to drill holes or anything and they just pop right in.

Posted 1 month ago

Allan F

Every thing arrived in perfect condition, thanks to the very secure packaging. Windows fit as expected, although quite tight. After installation we noticed that the cold drafts were gone and the room felt a lot warmer. We are very satisfied with the product and the result.

Posted 1 month ago

Adriana W

Great customer service! Super satisfied with our windows.

Posted 1 month ago

Thomas M

Indow service and product is good. Reduced outside noise considerably.

Posted 2 months ago