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Secondary glazing with magnetic tape is a simple DIY way to make your home warmer, quieter, and more comfortable without replacing your windows. A clear acrylic panel is cut to size and attaches neatly to the window frame with magnetic tape, creating a sealed air gap that helps keep heat in, draughts and noise out, and reduces condensation on your windows. It’s almost invisible once in place, easy to remove in summer, and a smart way to cut energy bills while enjoying a more peaceful home without the cost, disruption, or permissions often required for new double glazing.
Our window insulation kit uses premium Perspex® acrylic cut to your exact size and a magnetic fixing system (steel strip on your frame, magnetic strip on the panel) so you can remove the panel when needed.
The insulating air gap helps prevent heat escaping through single (and even double) glazing. Customers commonly report a noticeable rise in room temperature after installation. Many recover the kit cost over a couple of winters through energy savings.
The extra layer and air gap dampen sound transmission. Paired with your existing window, acrylic secondary glazing panels can significantly reduce traffic and street noise. A smart, cost-effective alternative to replacing windows purely for soundproofing.
By keeping the inner surface warmer, secondary glazing helps reduce visible condensation on colder mornings. Ventilation still matters, but most users see fewer drips and clearer panes.
Slim, clear Perspex® (92% light transmission) preserves daylight and views. The magnetic fixings make the panel easy to remove for cleaning, spring ventilation, or summer storage.
Ideal where replacing windows isn’t allowed or desired. Typically, no planning permission is required because the panel is internal and removable (always check your local guidance).
Acrylic is impact-resistant and shatter-safe compared with glass, adding a subtle security layer to vulnerable ground-floor windows if drilled in place.
Mark from Lancashire installed our 4mm acrylic secondary glazing over existing double glazing. Within days he noticed his living room felt much warmer with a 4°C difference on his digital thermometers placed inside and outside the secondary glazing.
Mark told us: “I only have one month's figures to work on but a 4°C saving means it will reach breakeven point in the winter months of the first year.”
William from Edinburgh installed our 5mm acrylic secondary glazing on his sash windows. He noticed a significant improvement in both temperature and noise reduction.
William told us: “It is difficult to say if the thermal insulation or the sound reduction is better. Both are outstanding. The noise reduction is significant. We live on a busy road with two bus routes and we are sleeping much better now with the 5 mm secondary glazing.”
Maureen from Southampton installed our 4mm acrylic secondary glazing to her conservatory, 12 windows in total. Maureen can now happily sit in her conservatory and use it as intended.
She told us: “My conservatory always felt cold and damp, although it has radiators, now it's feeling warm and dry. Pleased I did it!”
As a rule of thumb, thicker panels feel stiffer, insulate a touch better, and block more noise — especially on larger panes.
| Thickness | Best for | Tape | Notes |
|---|---|---|---|
| 3mm | Small windows (a perimeter of less than 4500mm) | Small Tape | Good balance of clarity, weight and stiffness for everyday use. |
| 4mm | Medium to larger windows (a perimeter over 4500mm) | Large Tape | Popular all-rounder for living rooms & bedrooms. |
| 5mm | Large windows and/or high-traffic, noisy locations | Large Tape | Customers report better noise reduction. This will be heavy so will need a sill/ledge support. |
Tip: For very large panes, choose 4–5mm acrylic and rest the panel on a sill or discreet baton so the magnets aren’t supporting all the weight.
We can cut ANY size or shape — circles, arches, L-shapes and more. Use the upload feature and upload a DXF or .ai file. Don't have a DXF or .ai file? No problem, for a small design fee, we can turn your sketch or image into a cut-ready DXF file for you.
Fitted perfectly, easy to put up and has made a massive difference to the temperature of the room.
No drilling for standard, vertical windows)
Step 1: Clean the frame ready for application.
Step 2: Measure and cut the steel tape (thinner tape) for the window frame. For a cleaner look in the corners, you can cut the steel tape at a 45-degree angle for a mitre join.
Step 3: Apply the steel tape (Side A) to the window frame. Make sure to leave no gaps in the corners so that it is as air-tight as possible.
Step 4: Stick Side B on top of the previous strips.
Step 5: Remove the protective film from one side of the acrylic.
Step 6: Peel off the backing from Side B to expose the adhesive. Align the acrylic piece with the tape, and press it to the side from which you have removed the protective film against the adhesive surface.
Step 7: Take off the second protective film to reveal your clear secondary glazing sheet installed!
Important: Magnetic fixing is designed for vertical windows. We do not recommend magnets for rooflights or sloped windows, as gravity may overcome adhesion.
Download Installation Guide
Share your Secondary Glazing photos with us to feature on our website. Simply mention @cutmy.uk on Instagram or upload a photo and tag us!
Here are a few tips to help you maintain the quality of your glazing and keep it functioning smoothly:
Store the Glazing Sheet Flat
When storing your secondary glazing acrylic sheet, keep it flat to avoid bowing. If you must store it upright, ensure it’s supported to stay flat and aligned vertically. Wedge it between a wall and furniture or tuck it behind a cabinet.
Addressing Bowed Glazing
If your glazing sheet has developed a slight bow after storage, don’t worry! Leave it in a position that encourages it to bend in the opposite direction. Check periodically to see when it has straightened out.
Avoid High Temperatures and Opposing Magnetic Fields
Magnetic tape can lose effectiveness if exposed to high temperatures or nearby opposing magnetic fields. Store it in a cool, dry place away from interfering items.
Keep the Magnetic Tape Clean
Dust and dirt can weaken the bond between the magnetic tape and the window frame. Periodically wipe both with a damp cloth to remove debris, and ensure they are dry before reinstalling the glazing.
Replace Worn Magnetic Tape
Magnetic tape can lose its adhesive properties over time, especially with high temperatures or frequent reinstallation. Regularly inspect for wear, like peeling or weakened magnetic strength, and replace as needed for a strong hold. You can easily purchase replacement magnetic tape from us if you need to.
For more detail, please see our guide on how to store your secondary glazing to prolong its lifespan. If you have any concerns or questions, feel free to contact us.
| Material | Acrylic |
| Finish | Clear |
| Maximum Sheet Size | 3050mm x 2030mm |
| Available Thicknesses | 3mm, 4mm, 5mm |
| Light Transmission | > 92% |
| Fire Rating | UK Class 3 Fire Rating |
| Water Absorption | 0.2% (24 h, 23oC) at dry state 50 x 50 x 2mm – 40mg to ISO 60, Method 1 |
| Manufacturers Tolerances | +/- 10% plus 0.4mm (e.g. 5mm cast sheet could vary from 4.1mm to 5.9mm) |
| Cutting Tolerances | +/- 1mm |
No, the magnetic tape is not included. You will need to add magnetic tape to your order by selecting the required size tape in the Magnetic Tape dropdown above. When selected the required amount of tape will be added to your cart.
Yes — and we have the proof. By adding a Perspex® acrylic panel inside your existing window, you create an insulating air gap that can raise the temperature of a room by several degrees. Even a 1°C improvement means you can turn down the thermostat and save money.
One of our customers, Mark from Lancashire, recently ran his own experiment after fitting a 4 mm secondary glazing panel to his sitting room:
“Rather than replace my old double glazing, I spent under £200 on a secondary glazing sheet. Using two digital thermometers I measured the difference: around 4°C warmer inside compared with outside, and a further 4°C improvement between the air gap and my living room. It performs almost identically to my original double glazing.”
“The window side of the room is now the same temperature as the centre — no more cold spots. Based on this saving, I expect the glazing to pay for itself within the first winter.”
Mark even shared a photo showing a 5.3°C difference between the thermometer inside his room and the one behind the secondary glazing panel. His results back up what many customers find: secondary glazing is a low-cost way to make your home warmer, cut heating bills, and feel more comfortable straight away.
Secondary glazing can be done with a clear acrylic or polycarbonate sheet, attached into place with a removable fastener such as our magnetic tape, allowing you to remove the secondary glazing during the warmer periods.
This will depend entirely on the size of your window. For a window measuring 635 x 890 mm, which is a fairly common window size in the UK, our 3mm plastic secondary glazing kit would cost only £55.41 - when compared to the cost of buying new uPVC casement windows, labour costs, and a plasterer to refinish the internal areas round the window, you'll be saving hundreds.
We recommend 4mm for secondary glazing. This thickness offers improved insulation properties and enhanced protection against noise and drafts. It is a common choice for secondary glazing in residential buildings and provides a good balance between insulation and affordability.
2mm: Only to be used on very small windows. 2mm offers basic protection but may not provide significant insulation or soundproofing benefits.
3mm: A good budget option for small windows under 800mm, still lightweight and suitable for basic insulation and protection against drafts. It provides better durability than 2mm and more rigidity.
4mm: Our recommended thickness, you'll certainly notice the improved insulation properties and reduction in condensation, noise and drafts. Any window larger than 800mm will benefit from the rigidity of 4mm.
5mm: Thicker acrylic provides the maximum enhanced insulation and soundproofing benefits. It is suitable for areas where noise reduction and thermal insulation are crucial, such as homes located near busy streets or commercial areas. 5mm is ideal for large windows over 1.5m but it will be heavy so you'll need our thicker magnetic tape and a windowsill or wooden baton to rest it on to take the majority of the weight.
Due to the optical clarity that acrylic provides, there’s no noticeable difference between the visibility or light transmission of your single-glazed windows and the results of secondary glazing. Often a preferable alternative to double glazing, particularly for heritage properties, acrylic doesn’t detract from the external character and look of the windows but gives all of the insulating benefits without causing condensation.
We don’t recommend magnetic fixing for sloped windows — gravity can overcome adhesion.
When you install secondary glazing into your property, you achieve the same insulating benefits of double glazing such as lower energy bills and improved heat transfer. Secondary glazing can reduce heat loss via windows by around 65% which is 10% more than double glazing.
To attach your glazing to a window, you'll need to take precise measurements using a measuring tape. Measure both the height and width of the window, and don't forget to include the width of the magnetic tape. Keep in mind that windows are not always perfectly shaped, so it's important to take measurements in multiple places to ensure an accurate fit.
Secondary glazing can be very effective at preventing condensation and mould growth on windows in cold climates. However, this does work best if the secondary glazing has a breathable gap between the panes rather than a fully sealed unit. This allows some airflow which helps prevent the build-up of condensation.
As our secondary glazing kits are magnetic, you can simply remove the plastic sheet for quick and easy access for cleaning or extra ventilation.
Delivery depends on the size of your order
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