Quick answer: A magnetic secondary glazing kit uses white steel tape fitted around your window frame and brown magnetic tape fitted around a sheet of Perspex, so the two simply click together. It reduces heat loss, dampens noise, and typically pays for itself within a few months, all without hiring a tradesperson.
Draughty windows are an expensive habit. Every winter, heat slips out through old frames and single-glazed panes, leaving you with a chillier living room and a heftier energy bill. Full double glazing fixes the problem, but it's expensive, disruptive, and often impossible if you're renting or live in a listed building.
That's where DIY secondary glazing comes in. Rather than replacing your windows, you add a removable second layer of Perspex to the inside, held firmly in place with magnets. No specialist tools, no mess, and no need to wait weeks for an installer.
In this guide, we'll explain exactly how a magnetic secondary glazing kit works, walk through the installation process step by step, and run through the benefits that make it such a popular choice for homeowners, landlords, and renters alike.
What is a magnetic secondary glazing kit?
A secondary glazing kit is a two-part tape system designed to hold a sheet of Perspex (acrylic) securely over an existing window.
The kit includes:
- White steel tape with an adhesive backing, which is fixed around the inside of your window frame.
- Dark brown magnetic tape with an adhesive coating (protected by a red backing liner), which is fixed around the edge of your Perspex sheet.
Once both tapes are in place, the magnetic tape clings to the steel tape, holding the Perspex firmly against the frame. It's a genuinely clever bit of engineering disguised as a very simple product — no screws, no brackets, and no drilling into your window frame.
You'll need to source your own Perspex sheet separately, cut to size for your window, but everything else needed to fit it is included in the kit.
How does magnetic secondary glazing actually work?
The principle behind magnetic glazing is refreshingly straightforward: magnets attract steel.
Once the steel tape is stuck around your window frame and the magnetic tape is stuck around your Perspex sheet, you simply offer the Perspex up to the window and let the magnets do the rest. The magnetic adhesive tape grips the steel strip with enough force to hold the panel firmly in place, even in draughty or exposed rooms, while still allowing you to peel it off in seconds whenever you need to.
This creates a sealed air gap between your existing window and the new Perspex layer. That trapped layer of air is what does the real work, acting as an insulating buffer that slows down heat transfer and reduces noise transmission from outside.
Why fit DIY secondary glazing? The benefits explained
This is where the kit really earns its keep. Here's what you stand to gain:
1. Lower energy bills
Windows are one of the biggest sources of heat loss in a typical home. By adding a secondary layer of glazing, you reduce the amount of warm air escaping and cold air creeping in, which means your heating doesn't have to work as hard. Many customers find that a DIY secondary glazing kit pays for itself within a single winter through reduced energy costs.
2. Reduced noise
That extra air gap doesn't just trap heat, it dampens sound too. If you live near a busy road, a school, or noisy neighbours, secondary glazing can noticeably cut down on external noise, making your home a calmer place to be.
3. No professional installation required
Choose magnetic secondary glazing if you want results without the hassle of hiring a tradesperson. The whole system is designed for straightforward DIY fitting, so there's no need to book an installer, take time off work, or live with scaffolding outside your window for a week.
4. Fully removable and reusable
Unlike permanent glazing solutions, the magnetic fixing means your Perspex panel lifts straight off whenever you need it to, whether that's for cleaning, ventilation, or simply opening the window on a warm day. Pop it back on and the magnetic seal is instantly restored.
5. No damage to window frames
Because the system relies on adhesive tape and magnets rather than screws or drilled fixings, it's ideal for rented properties, listed buildings, or anyone who simply doesn't want to make permanent alterations to their windows.
6. Budget-friendly compared to full double glazing
Replacing single glazing with full double glazing can cost thousands of pounds per window. A magnetic secondary glazing kit delivers many of the same thermal and acoustic benefits at a fraction of the price, plus you only need to buy the Perspex to complete the job.
7. Neat, low-profile finish
The slim steel tape and flexible magnetic tape sit discreetly around the window frame, so the finished result looks tidy rather than bulky or industrial.
8. Suitable for a range of window shapes and sizes
Because the tapes are flexible, they can be fitted around most standard window shapes, including larger openings, as long as the Perspex panel is cut to match.
How to install your magnetic secondary glazing kit
Choose this method if you want a weekend project rather than a major renovation. Here's the process from start to finish:
Step 1: Measure your window.
Measure the inside of your window frame carefully, noting height and width at multiple points in case the frame isn't perfectly square.
Step 2: Order your Perspex.
Using your measurements, have a Perspex sheet cut to size. This is purchased separately from your secondary glazing kit.
Step 3: Clean the window frame.
Wipe down the frame surface to remove dust, grease, or debris. A clean surface helps the adhesive-backed steel tape bond properly.
Step 4: Apply the steel tape to the frame.
Peel back the adhesive liner and press the white steel tape firmly around the inside edge of the window frame, following the full perimeter.
Step 5: Apply the magnetic tape to the Perspex.
Peel off the red backing liner from the brown magnetic tape and stick it around the edge of your Perspex sheet, lining it up with where the steel tape sits on the frame.
Step 6: Attach the Perspex to the window.
Offer the Perspex panel up to the frame and press gently around the edges. The magnetic tape will grip the steel tape and hold the panel securely in place.
Step 7: Check the seal.
Run your hand around the edge to make sure the magnetic connection is continuous, with no gaps where draughts could sneak through.
That's it — no silicone, no screws, and no waiting for anything to cure or dry.
What length kit do you need?
Magnetic secondary glazing kits are supplied in rolls, so the length you need depends on the total perimeter of the windows you're fitting. Add up the perimeter of each window you plan to cover, then choose a roll length to match.
30m rolls are our most popular option, as they tend to cover several average-sized windows in one go, making them good value if you're fitting more than one room. Larger quantities are also available if you're covering a whole house, while shorter rolls work well for single, smaller windows.
If you're not sure how much you need, measure first and round up slightly. A little spare mag tape is always more useful than running short halfway through a window.
Ready to stop paying to heat the outdoors?
Fitting a magnetic secondary glazing kit is one of those rare home improvements that's genuinely quick, affordable, and effective. You get warmer rooms, quieter surroundings, and a tidier energy bill, all without a single drill hole in your window frame.
Measure up, choose your roll length, and get your Perspex ordered. Click here to buy now and have your windows draught-proofed before the next cold snap arrives.
Frequently asked questions
Does magnetic secondary glazing actually keep heat in?
Yes. The sealed air gap created between your existing window and the Perspex panel acts as an insulating barrier, reducing the amount of heat that escapes through the glass and frame.
How much does a DIY secondary glazing kit cost compared to double glazing?
A magnetic secondary glazing kit costs significantly less than replacement double glazing, since you're only paying for the tape system and a Perspex sheet rather than entirely new window units and professional fitting.
Can I remove the Perspex panel whenever I like?
Yes. Because the panel is held in place magnetically rather than fixed permanently, it can be lifted off and reattached as often as needed, for cleaning, ventilation, or seasonal use.
Will the tape damage my window frame?
The steel tape is adhesive-backed but designed for interior frame surfaces, making it a low-impact option that doesn't require drilling or screwing into the frame.
Who is DIY magnetic secondary glazing best suited for?
It's a strong option for renters, listed building owners, and anyone wanting a budget-friendly, non-permanent alternative to full double glazing, particularly where drilling or structural changes aren't possible.
What size roll should I buy?
Measure the total perimeter of the windows you're covering. For multiple average windows, a 30m roll is usually the most cost-effective option; smaller or larger lengths are available depending on your needs.