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FINEO, Heritage Slimline, or Planitherm: Which Glass is Best for Your Double Glazed Sash Windows?

Updated: Jul 3

When it comes to preserving the charm of traditional sash windows while enhancing energy efficiency, UK homeowners have several excellent double glazing options to choose from. At Classic Sash Windows, we specialise in offering a variety of double glazed sash windows, each tailored to meet different needs and preferences. In this article, we'll compare three leading types of double glazed glass: FINEO, heritage slimline double glazed units, and Planitherm. Understanding the strengths and features of each can help you make an informed decision for your home.

The Importance of Double Glazed Sash Windows

Double glazed sash windows are an increasingly popular choice among UK homeowners, particularly those with older properties. These windows maintain the aesthetic appeal of traditional sash windows while offering improved thermal performance and noise reduction. The effectiveness of double glazing lies in its construction: two panes of glass separated by a layer of inert gas, which significantly enhances insulation compared to single glazing.

FINEO Glass: The Modern Marvel for Heritage Windows

comparison table showing benefits of FINEO glass compared to other glass types

FINEO glass is an ultra-thin vacuum glass that combines the best of both worlds: the aesthetic and structural characteristics of traditional single glazed windows with the thermal efficiency of modern double glazing. Here’s why FINEO glass stands out:

  • Ultra-Thin Profile: At just 6.7mm thick, FINEO glass is ideal for sash windows in heritage properties where maintaining the original look is crucial.

  • Superior Insulation: Despite its thin profile, FINEO glass offers excellent thermal insulation, comparable to traditional double glazing.

  • Lightweight: The lightweight nature of FINEO glass means it can be installed in existing frames without compromising the structure.

  • Longevity: Designed to last, FINEO glass boasts a lifespan comparable to traditional double glazing units.

Heritage Slimline Double Glazed Units

diagram of heritage slimline double glazed units

For those seeking a more traditional double glazing option, heritage slimline units offer a perfect solution. These units are designed to replicate the look of original sash windows while providing the benefits of double glazing. Here’s what makes heritage slimline units a great choice:

  • Aesthetic Appeal: The narrow sightlines and slim profile ensure that the windows look as close to the originals as possible.

  • Energy Efficiency: They offer significant improvements in thermal performance over single glazing, helping to keep your home warm and reduce energy bills.

  • Noise Reduction: Heritage slimline units provide better acoustic insulation, making your home quieter and more comfortable.

  • Compatibility: Specifically designed to fit into existing window frames without altering their historic appearance, making them ideal for conservation areas and listed buildings.

Planitherm Slimline Double Glazing

Planitherm is known for its high-performance glass solutions that enhance both comfort and energy efficiency. Here’s why Planitherm slimline double glazing is worth considering:

  • Exceptional Thermal Insulation: Planitherm glass offers outstanding thermal insulation, reducing heat loss and lowering energy bills.

  • Optimized Light Transmission: Planitherm glass ensures high levels of natural light while minimizing glare, creating a bright and comfortable living environment.

  • Low-E Coating: The low-emissivity coating on Planitherm glass reflects heat back into your home, enhancing its thermal efficiency without compromising the traditional look of your sash windows.

  • Slim Profile: Designed to fit into traditional sash window frames, Planitherm slimline units preserve the historic appearance of your windows while providing modern benefits.

Why Choose Classic Sash Windows?

At Classic Sash Windows, we understand the importance of preserving the character of your home while upgrading its functionality. We offer a range of double glazed sash windows, including FINEO glass, heritage slimline double glazed units, and Planitherm slimline double glazing, ensuring that you can find the perfect solution for your property. Our expert installation team ensures a seamless fit, maintaining the integrity and beauty of your windows.


Choosing the right type of double glazed sash window glass is crucial for maintaining the historic charm of your home while enhancing its energy efficiency and comfort. Whether you prefer the ultra-thin and lightweight FINEO glass, the traditional aesthetics of heritage slimline units, or the high-performance benefits of Planitherm, Classic Sash Windows has the perfect solution for you. Contact us today to learn more about our installation services and find the ideal double glazed sash windows for your property.


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