My uPVC double-glazed bay windows each have what appears to be two approx 3.5 cm diameter (1 3/8") vertical aluminium cylindrical poles on either side of the central window pane of the three panes that make up each bay window.

In winter (UK, so temperatures are rarely below freezing) these get cold and contribute to condensation problems and heat loss. Not a good design and I'd rather replace it entirely, but unfortunately that would involve third parties and a lot of admin, as would solving it with insulation on the external side.

I'm thinking to insulate them internally with maybe uPVC channel or strip of some sort filled with foam, but I fear it would look pretty bad if I got enough depth of insulation.

How much insulation depth would be needed to prevent consensation on these? Can I insulate them without replacing the poles without it looking bad?

Vertical pole between uPVC window frames

  • 1
    "looking bad" is entirely subjective.
    – Ecnerwal
    Commented Aug 28, 2022 at 13:51
  • 2
    Can you post a photo of the aluminum? I've having difficulty imagining the exact shape and relationship to the window pane.
    – Armand
    Commented Aug 28, 2022 at 21:38
  • Good idea thanks, I'll figure out how to add a photo. Looking again I wonder if in fact it's uPVC. Certainly not steel (non-magnetic), but I assumed painted Aluminium because of how cold it feels in winter, but perhaps it's just the hollow cross section that's to blame for that. If I'm wrong and it's uPVC, perhaps just filling it with insulating foam would help a lot! Very useful comment just based on that possibility... Commented Aug 29, 2022 at 15:20
  • It is uPVC! I pried away some uPVC strip at one end that needs replacing on one of the windows and dug in with a knife where it won't be visible later. I would never have noticed if you hadn't asked, thanks again. I guess just drilling holes and filling with expanding foam (or just exposing the top and filling from there) is a good way to insulate this... Commented Aug 29, 2022 at 15:33

2 Answers 2


You can certainly insulate them - even 5-6mm thickness of foam insulation would make a significant difference .vs. an aluminum part without a thermal break. Even if it does not eliminate all condensation, it would reduce it quite a bit. It may be enough to eliminate it.

A foam tape product might be worth trying (applied when the poles are dry.)

  • 1
    Thanks. Foam wouldn't look good on it's own. I'm not sure I can stomach making that same objective point in a way that doesn't trigger your/SE's "subjectivity language" buttons, though ;-) Commented Aug 28, 2022 at 20:28
  • The problem with "looks good" is that it's a matter of individual taste. Perhaps there's a uPVC part that would cover it up. I'd probably look towards a thin wood veneer over it, but then, plastic window interiors are not much to my taste, so I have wood interior/fiberglass exterior windows to suit my individual taste in not having plastic window frames inside the house, while having a low maintenance exterior frame.
    – Ecnerwal
    Commented Aug 28, 2022 at 22:40
  • uPVC covering: so far I've not found something suitable (despite having bought similar materials in the past). I do feel it must be out there somewhere though. Or perhaps there's some insulation product with a finish on it? "Individual taste": that isn't true when it comes to the level of "decorate your house in foam insulation", right? I think when people use words like "wouldn't look good" here, they're likely not talking about fashion advice or style guidance, they're just talking about a decent finish and an acceptable appearance by commonly accepted standards of the time. Commented Aug 29, 2022 at 15:00

The only thing we can do for you, is recommend insulating techniques. It's up to you to select one that "looks good" to you. Or, possibly, "looks least bad", as slapping insulating material on a part of a window will likely look bad no matter how you approach it.

With the thought that anything applied to part of the window/frame may end up looking pretty shoddy, I would suggest looking at applying an insulating layer over all the "woodwork" of the window.

Take a piece of insulation (foam would be good, ensure that it's approved for use in your area - remember, some foams can give off toxic fumes should they be exposed to flame), cut it to the size of the window, then lay out all of the frame lines, sash, and mullion bars, etc, then cut out the openings where the actual glass go.

Now you have a duplicate of the window's "woodwork" made out of foam. Attach this with some double stick tape to the actual window frame. The "woodwork" is now deeper than it was, but it's still consistent across the entire window. If desired (and you have some skill), you could cut a profile into the foam to match the profile of the existing windows. (This site (first result of an internet search) shows some traditional (US) patterns to show what I'm talking about). You could approximate these in foam if you already have them, or you could spruce things up a bit by applying a profile where none existed before if you wanted.

It sounds like you have a 3-window unit, so you'd need to duplicate this process for all 3 windows at this location to keep the appearance consistent.

Since insulation foam (in the US, at least) is usually pink, blue, or green, and those colors probably don't go well with your decor, enhancing the "ugly" factor. Prior to installation, paint them (spray paint designed for plastics should do the trick) an appropriate color.

  • "Or, possibly, "looks least bad", as slapping insulating material on a part of a window will likely look bad no matter how you approach it." -- I see you do understand this part of the question Commented Aug 29, 2022 at 15:03
  • "Prior to installation, paint them" -- thanks, interesting idea given the lack of success I've had looking for uPVC and the extra depth that would be added by a uPVC covering on the foam (presumably at lower insulating efficiency than the foam). I've not seen insulation foam with a smooth surface. Perhaps some are smooth enough that suitable paint would make them smooth enough that that isn't very noticeable to most people? Commented Aug 29, 2022 at 15:13
  • You may have to apply additional coatings of material to the foam to get a suitable surface for painting. Unfortunately, I don't think there will be an "easy" solution.
    – FreeMan
    Commented Aug 29, 2022 at 17:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.