Green Building Forum - Multifoil -- finally he does it! Mon, 02 Nov 2026 04:23:11 +0000 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38555#Comment_38555 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38555#Comment_38555 Tue, 18 Nov 2008 12:26:20 +0000 biffvernon Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38556#Comment_38556 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38556#Comment_38556 Tue, 18 Nov 2008 12:30:16 +0000 Saint Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38565#Comment_38565 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38565#Comment_38565 Tue, 18 Nov 2008 14:10:08 +0000 Matt Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38614#Comment_38614 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38614#Comment_38614 Tue, 18 Nov 2008 18:47:39 +0000 tony
Did I show newspaper multilayer is as good as multifoil or do I need to some more?]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38623#Comment_38623 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38623#Comment_38623 Tue, 18 Nov 2008 19:20:18 +0000 Mike George
One of the problems with any lab tesing [such as the hot plate] is that it gives no consideration to air tightness, hence, the better k-values published.

Presumably your testing does not allow for air tightness either? so it is not surprising to me that you have the results you report.

I have yet to hear anyone prove or disprove the argument for airgaps or the radiant heat transfer part of the eqation.

Not wishing to hyjack the thread but I have also conducted comparative simulation testing with Tas with results which reinforce the MF manufacturers claims. The trouble is that I cannot explain why the results are as they are -and the research has come to a grinding halt. I need someone with a greater understanding of the alogrithms and physics involved- anyone want to take a look at the results? I posted the results on the MF thread some time ago. To date no-one has conducted any thermal modelling which questions my methodology or the results obtained.]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38635#Comment_38635 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38635#Comment_38635 Tue, 18 Nov 2008 19:50:24 +0000 biffvernon
But hey! Let's get back to the real thread :)

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&page=13]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38638#Comment_38638 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38638#Comment_38638 Tue, 18 Nov 2008 19:53:51 +0000 Mike George Posted By: biffvernonAnd nobody has been able to explain how the internal foils do anything other than boost the profits of the manufacturers.



Agreed]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38656#Comment_38656 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38656#Comment_38656 Tue, 18 Nov 2008 20:43:03 +0000 djh

But I'm not sure anybody has changed their opinion. That was my point that Biff questioned. I agree that the IR doesn't need an inch or two of space to make its mind up, and I can't be arsed to argue whether its lambda or lambda/2 or lambda/4 or whatever that it does need. But I think that people who do believe in multifoil will dismiss Tony's experiment because it didn't have the air gaps, so I'm not sure how much is achieved.

BTW, I have a copy of a very nice paper about *real* multifoil insulation. It demonstrates its amazing properties in ultra-high vacuum and close to abolute zero temperature and has a nice graph showing how all that wonderful behaviour disappears as the atmosphere is allowed to leak back in. :devil:]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38665#Comment_38665 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38665#Comment_38665 Tue, 18 Nov 2008 20:48:08 +0000 fostertom Posted By: biffvernonYou are measuring the temperature gradient from a warm place to a cold place, but not measuring the rate of energy flow along that gradientCorrect. So far, this v interesting experiment says nothing, either comparatively or absolutely, about the rate of flow of heat in any of the variants. It does throw light on the temp gradient's distribution from layer to layer in the different variants, and it throws light on Biff's contention that the inner layers of foil do next to nothing:
Posted By: biffvernonSuggest you keep foils 1 and 6 and just replace the internal foils, 2-4, with paper. It's the added value of the internal foils that are the real issue. The outer ones probably are worth the money
because if the inner layers do next to nothing then the temp difference between any two of them wd be small to zero. On these results, that's not so - temp differences between all layers are of the same order, though irregular.

I'm all set to say more, but need some clarification, Tony.
Posted By: tonyPut my temperature probes in between the layers
but your diagrams seem to show the temps of the foils, not of the gaps between. Are you assuming that the temp between a foil and a wadding is same as the foil's temp? Not so. It wd be interesting to put sensors into every gap, not just alternate ones - then you'd see whether the foil or the wadding was creating most of the drop between adjacent layers.

In the first two cases, one outer foil seems to be free, at different temp to the cold source (room), but the other outer foil is at same temp as the hot source - in gapless contact with the hot plate? Or if gap between hot plate and foil, did you put a sensor between and assume that was the foil's temp? Can't be - both the hot-side outer foil and even more the gap between it and first wadding must be lower than the hot plate. The effect of this experimental error is to diminish the %age of the total temp drop that's apparently contributed by the inner layers - but despite this in all the variant cases the inner layers clearly do approx their full share pro rata.

In the third case - re-run of the second, it looks like replacing the wadding with newspaper has now not impared, but greatly improved the inner foil layers' ability to resist heat transfer, relative to the two outer layers'! Which one (second or third) to believe? And which one to take as comparison base to the fourth case?

In the fourth case, there's one too many readings, compared to previous, plus a contradiction - says 'hot plate 74' but first reading is 72.

Apart from that, great, very instructive. I'll say again, my suggestion is to put sensors into every gap of standard multifoil, not just alternate ones - then you'd see whether the foil or the wadding was creating most of the drop between adjacent layers. Seems to me you can't measure the temps of the layers, only of the gaps between *all* layers, plus room temp, plus hot plate temp but not the gap between hot plate and first foil - get clear about that and we'll get some useful results.]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38673#Comment_38673 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38673#Comment_38673 Tue, 18 Nov 2008 20:52:10 +0000 jon
However, internal foil seems to me to be a complete waste of effort: For the reason that if damage occurs to an area, or if there are gaps between boards, the foil itself provides a conductor to take away heat at a much faster rate from well insulated surfaces to these higher loss areas than had it not been there at all.

The idea of putting something there, but not foil, to get a better airseal seems very sensible.]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38675#Comment_38675 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38675#Comment_38675 Tue, 18 Nov 2008 20:59:15 +0000 fostertom Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38677#Comment_38677 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38677#Comment_38677 Tue, 18 Nov 2008 21:00:33 +0000 Mike George Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38679#Comment_38679 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38679#Comment_38679 Tue, 18 Nov 2008 21:05:11 +0000 jon
If it's plastic, sounds sensible Tom. I don't know what the shiny stuff is either but assumed it was metallic: Is that not so?

Even a fraction of a millimetre could conduct heat very efficiently.

I thought of using something like Celotex (in layers) for a rather specialist application I'm developing but the surface conductivity was too high (from the readings I got). Would be interesting to know what the 'multifoil' material is]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38690#Comment_38690 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38690#Comment_38690 Tue, 18 Nov 2008 21:23:26 +0000 fostertom
Posted By: jonEven a fraction of a millimetre could conduct heat very efficiently
i don't get it - what origin or kind of temp gradient wd drive heat along the plane of the foil?]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38698#Comment_38698 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38698#Comment_38698 Tue, 18 Nov 2008 21:42:59 +0000 biffvernon Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38704#Comment_38704 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38704#Comment_38704 Tue, 18 Nov 2008 21:52:17 +0000 fostertom Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38707#Comment_38707 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38707#Comment_38707 Tue, 18 Nov 2008 21:54:42 +0000 fostertom Posted By: biffvernonThe shiny stuff is alluminiumWell, blow me. What's mylar then - surely not metallic? If metallic, does multifoil in fact block mobile signals? This wd have significant health implications, prob for both good and bad.]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38709#Comment_38709 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38709#Comment_38709 Tue, 18 Nov 2008 21:57:41 +0000 Matt Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38712#Comment_38712 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38712#Comment_38712 Tue, 18 Nov 2008 22:03:58 +0000 Mike George Posted By: biffvernonThe shiny stuff is alluminium.

How do you know Biff?]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38714#Comment_38714 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38714#Comment_38714 Tue, 18 Nov 2008 22:17:16 +0000 Paul in Montreal Posted By: Mike GeorgeHow do you know Biff?

The specs for the stuff we get over here - not really multifoil but "double-bubble" state that it is 99.9% alumin(i)um. I found this out for sure when I accidentally touched a live electrical cable to some I'd installed - huge sparks and a change of underwear for me!

Thin metal foils are transparent to an extent - ever seen those gold windows in 1970s office blocks? The people inside and see out. And don't forget about one-way mirrors - they're either silver or aluminium and you can easily see through.

For the foils to block phone signals they'd have to be grounded. Even then, it is somewhat dependent on the frequency of the signal since there is always an opening somewhere (window, door etc.).

Paul in Montreal.]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38715#Comment_38715 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38715#Comment_38715 Tue, 18 Nov 2008 22:20:53 +0000 Paul in Montreal Posted By: fostertomWell, blow me. What's mylar then - surely not metallic? If metallic, does multifoil in fact block mobile signals? This wd have significant health implications, prob for both good and bad.

It would have no health implications as there is no demonstrable link between electromagnetic radiation and health (psychosomatic effects notwithstanding and obviously not including such radiation as X-rays, microwave in the oven frequency etc.). Mylar is the trade name for a polyester film. It's a good substrate for applying a metal coating (like in those survival blankets you see).

See http://en.wikipedia.org/wiki/PET_film_(biaxially_oriented)

Paul in Montreal.]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38716#Comment_38716 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38716#Comment_38716 Tue, 18 Nov 2008 22:37:34 +0000 fostertom Posted By: Paul in Montrealno demonstrable link between electromagnetic radiation and healthAh come on!

Posted By: Paul in MontrealMylar is the trade name for a polyester film. It's a good substrate for applying a metal coating
I see.]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38719#Comment_38719 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38719#Comment_38719 Tue, 18 Nov 2008 23:16:38 +0000 Mike George
Should say that some I have tried do not lose their coating at all so may be a different material altogether.

I have tried to find out the exact composion of multifoils several times- manufacturers are not forthcoming.]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38721#Comment_38721 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38721#Comment_38721 Tue, 18 Nov 2008 23:31:18 +0000 jon
Imagine the thermal conductivity of alu is about 200 (so it's about 20C as the conductivity of alu varies)
Your insulation might be 0.03
Let's say the film is 10 microns (10 millionths of a metre) thick, so along a 50mm path, 50mm wide the loss of heat over a constant gradient is, more or less, proportional to: 10 E-3 x 50 x 300 = 150
A bit of insulation 50 by 50 by 50 is, along the same gradient 50 x 50 x 0.03 = 75
So, given the choice between the heat going through the insulation or along the film, it will always "choose" the film at the perimeter
(I had to re-do these figures when I realised I'd been mistakenly working in Kelvin.. when you work in the lower Kelvin range, the figures look really scary as the alu starts to tend towards being a superconductor)

Even if it were 100mm it would choose the film so this means that exposed joints might make panels work less well if the alu were exposed. It would be OK if everything were constructed perfectly without any errors though.]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38723#Comment_38723 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38723#Comment_38723 Tue, 18 Nov 2008 23:53:20 +0000 fostertom
However on a macro scale I don't see why heat would want to flow laterally, in the plane of the foil, when the temp gradient is perp to it.]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38724#Comment_38724 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38724#Comment_38724 Tue, 18 Nov 2008 23:55:45 +0000 CWatters Posted By: Mike GeorgeI have always held the opinion that the tests conducted by the MF manufacturers show multifoil and mineral wool as having similar heat losses mostly because of the vastly improved airtightness a multifoil will achieve.

Is that true though? Why doesn't the plastic plastic vapour barrier used with conventional insulation achieve the same airtightness? Perhaps because builders tape the joints on MF but are too lazy to tape a vapour barrier?]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38725#Comment_38725 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38725#Comment_38725 Wed, 19 Nov 2008 00:00:15 +0000 CWatters Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38726#Comment_38726 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38726#Comment_38726 Wed, 19 Nov 2008 00:13:07 +0000 fostertom Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38730#Comment_38730 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38730#Comment_38730 Wed, 19 Nov 2008 02:53:25 +0000 Gotanewlife
I know, I know, this is my Trombe wall question, not very well disguised, but above you are jumping all over my issue without quite stepping on it - and I could really use your opinions.]]> Multifoil -- finally he does it! https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38733#Comment_38733 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2952&Focus=38733#Comment_38733 Wed, 19 Nov 2008 07:36:33 +0000 Mike George Posted By: CWatters
Posted By: Mike GeorgeI have always held the opinion that the tests conducted by the MF manufacturers show multifoil and mineral wool as having similar heat losses mostly because of the vastly improved airtightness a multifoil will achieve.


Is that true though? Why doesn't the plastic plastic vapour barrier used with conventional insulation achieve the same airtightness? Perhaps because builders tape the joints on MF but are too lazy to tape a vapour barrier?

Maybe the case in real life situations. Also there are many layers in the MF- less likely to be sufficiently damages as to allow air through?

Also possible that ventilation on the cold side affected the manufacturers comparative resuts by 'blowing through' the mineral wool ?

Maybe the radiant heat transfer/air space part of the equation contributes also, but to what extent I don't know.]]>