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What is WindowSLIP?
WindowSLIP stands for Slim Line Insulating Pane. It is a high-performance, sash-mounted secondary glazing system designed to convert single-pane windows into simulated double-pane windows.
Unlike temporary window films, magnetic inserts, or bulky storm windows, a SLIP is a permanent architectural solution. Each unit features a slim-profile aluminum frame and high-performance glass that mounts directly to your existing sash. This design creates a sealed, insulating air space that modernizes the thermal performance of your building while remaining virtually invisible.
Our Origin Story
For decades, owners of historic homes and commercial buildings faced a difficult binary choice: keep their beautiful, original windows and suffer from drafts and high energy bills, or rip them out for vinyl replacements that destroy the building’s character.
Existing alternatives left much to be desired. Storm windows often block functionality, preventing you from easily opening your windows for fresh air. Plastic films and temporary inserts are often ineffective “band-aid” solutions that require annual replacement.
We recognized a gap in the market for a product that could bridge the divide between preservation and performance. We developed WindowSLIP to allow building owners to keep their dense, old-growth wood windows—which are often rot-resistant and irreplaceable—while achieving modern energy efficiency standards.
Since the inception of Window SLIP, SLIPs have been installed on hundreds of buildings throughout the USA! See some examples below:
“The SLIP Was A Game Changer For Me And My Family.”
It’s ingenious and I would recommend it to anyone who’s wanting to keep their vintage windows but upgrade their insulation. I’m a PNW gal and they’ve just made a world of difference. Thank you Chosen for the great product – I couldn’t be happier!
“Loved The Fact That I Could Keep My Vintage Windows And Update Them”
With my old storm windows that I had I didn’t have full operation of some of my windows but now that chosen came by all of my windows have full operation and I’m saving money o heat! The combination of slip and weatherstripping is night and day.10/10 would recommend
“Very Good Product”
11 out of 10 these guys are very knowledgeable and they have a very good product their installers are excellent craftsmen I would definitely recommend them for all of your vintage wood window needs.
“Hats Off To These Guys!”
This product is amazing!! I live in a house built in 1930’s and Chosen was able make my windows more efficient, saving me money each month on my electrical bill.
“Would Give A Sixth Star If Possible!”
Wonderful product for my wood windows. Friendly associates.
REDUCE YOUR WINDOW ENGERY BILLS BY UP TO 72%
Reach out & we’ll answer any questions you have to help you get started.
How Do Our Window SLIPs Work?
Window SLIPs are custom-made to fit the exact specifications of your residence or business. They are installed by contractors, architects, or licensed professionals. Because of their slim lines and clear glass– they’re nearly invisible once put on your window.
Custom Fabrication
Each SLIP is custom-fabricated to match the daylight opening of the sash and mounts securely to the interior or exterior face of the sash, depending on configuration. The system includes a slim-profile aluminum frame and high-performance glass, installed by trained contractors or preservation professionals. The low-profile frame can be painted to match your window and disappear. This allows your original window to show through as if no alterations were made.
Professional Installation
Windows remain fully operable, and in some cases, painted-over or damaged windows can be fixed utilizing Window SLIPs. Our systems come with all installation hardware included. In your package you’ll find hanging balances, weatherstripping, screws, and tabs.
Questions about Installation? Check out our Frequently Asked Questions page or this how-to video.
Energy Saving Benefits
The homeowners experience all the benefits of double-pane windows, without the price tag of full replacement. Our customers report cost savings of over 72% on their energy bills. They also notice reduced noise and no more moisture.
Proven Performance: The University of Oregon Study
We don’t just claim efficiency; we have tested it. WindowSLIP collaborated with the University of Oregon’s Energy Studies in Buildings Laboratory to validate our performance.
In a case study performed at Straub Hall, the laboratory compared WindowSLIPs against full Insulated Glass Unit (IGU) conversions. The results confirmed that SLIPs provided nearly identical levels of thermal insulation to full glass conversion, but at a significantly lower cost and with better preservation of the historic material.
Data from these studies indicates that installing SLIPs can result in energy cost savings of up to 72%.
Backed by Chosen Wood Window Maintenance
This product was not invented by a factory manufacturing line, but by restoration contractors who have spent over 20 years repairing and retrofitting wood windows. We designed the WindowSLIP system “by contractors, for contractors,” ensuring it respects traditional joinery and meets the rigorous standards required for historic preservation.
Whether you are a homeowner, an architect, or a facility manager, WindowSLIP offers a contractor-grade solution that respects the past while building for a sustainable future.