Green Building Forum - Multifoil Insulation Mon, 25 May 2026 15:57:15 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227957#Comment_227957 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227957#Comment_227957 Fri, 31 Jul 2015 15:36:34 +0100 Ian1961
Yes, I suppose you're right as other factors may have meant that the buildings heating system was able to perform okay in the completed building - for example this particular job was done well before any of the current requirements to pressure test and account for air leakage yet we paid a lot of attention to getting good air tightness. It's quite possible that better than expected air-tightness compensated for any under-performance in the Triso insulation.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227958#Comment_227958 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227958#Comment_227958 Fri, 31 Jul 2015 15:41:08 +0100 Mike George Posted By: Ian1961It's quite possible that better than expected air-tightness compensated for any under-performance in the Triso insulation.

That's my view. :cool:]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227960#Comment_227960 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227960#Comment_227960 Fri, 31 Jul 2015 15:51:40 +0100 SteamyTea

I think this does highlight the problems with comparing things that are not identical.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227962#Comment_227962 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227962#Comment_227962 Fri, 31 Jul 2015 15:58:04 +0100 Ian1961 In use, any feedback from occupants?"

It had stitching at intervals to hold the layers together.

Feedback - generally, as a building the client was absolutely delighted but that was more to do with the final look and quality of finishes, although we would have been the first to find out if the heating system hadn't performed as designed or if the house had been draughty.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227963#Comment_227963 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227963#Comment_227963 Fri, 31 Jul 2015 16:01:02 +0100 Mike George Posted By: Ian1961we would have been the first to find out if the heating system hadn't performed as designed or if the house had been draughty.

May have still been in the days when M&E tended to oversize though.....]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227964#Comment_227964 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227964#Comment_227964 Fri, 31 Jul 2015 16:12:26 +0100 SteamyTea
“The good thing about science is that it's true whether or not you believe in it.” Neil deGrasse Tyson]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227965#Comment_227965 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227965#Comment_227965 Fri, 31 Jul 2015 16:25:34 +0100 Mike George Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227966#Comment_227966 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227966#Comment_227966 Fri, 31 Jul 2015 16:31:34 +0100 Ian1961
I've got no axe to grind either way re multifoils

In the case of the building I described it was listed so we didn't have many alternatives to a multifoil and I would use it again in similar circumstances. It was a huge house with the Triso multifoil being the only insulation and we had no complaints at all from the client about the buildings performance.

At the moment, however, I'm designing my first ever new-build for myself (every architects dream!) on a lovely 1.5 acre plot in the clwydian range AONB in North Wales. I only got PP a few weeks ago so I'm still looking at detailed design but I will be specifying conventional insulation.

Ian]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227967#Comment_227967 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227967#Comment_227967 Fri, 31 Jul 2015 16:33:17 +0100 fostertom Posted By: Ian1961It had stitching at intervals to hold the layers together.In that case
Posted By: Ian1961 A lot of attention was paid to airtightness - taping etc.
was a waste of time, if that means taping the Triso joints. I once calc'd that those stitch holes are equiv to a 70mm diam hole per m2 of Triso. So let no one say that Triso's 'performance' is in any way due to the airtightness is provides (not) as a bonus.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227968#Comment_227968 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227968#Comment_227968 Fri, 31 Jul 2015 17:03:29 +0100 Mike George ]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227969#Comment_227969 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227969#Comment_227969 Fri, 31 Jul 2015 17:22:00 +0100 CWatters
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/2818/Building_regulations_determination_CI-45-1-238.pdf

selected quotes..

"BRE carried out direct measurements of the in-situ U-value of walls, roofs and floors in completed buildings incorporating multi-foil insulation. The measurements were made in accordance with the international standard ISO 9869. BRE concluded that the U-values measured in this way were broadly similar to the results obtained by NPL using the laboratory hot box method."

"More recent theoretical research by Professor Philip Eames of Loughborough University2, carried out for the Department after your full plans application was made, lends support to BRE’s conclusions...

snip..

To determine the best possible system performance that could be achieved using the best materials currently available, he repeated the calculations for multi-foil comprising polished silver foil and aerogel layers. The predicted U-values were:

•200mm mineral wool (no reflective backing): 0.17 to 0.19 W/m^2K
•100mm mineral wool (no reflective backing): 0.33 to 0.34 W/m^2K
•Multi-foil – typical (aluminium foil and foam): 0.35 to 0.50 W/m^2K
•Multi-foil – best possible (silver foil and aerogel): 0.23 to 0.27 W/m^2K"]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227970#Comment_227970 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227970#Comment_227970 Fri, 31 Jul 2015 18:17:48 +0100 ringi Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227975#Comment_227975 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227975#Comment_227975 Fri, 31 Jul 2015 20:14:24 +0100 fostertom Posted By: ringiIt's quite possible that better than expected air-tightness was BECAUSE of using the Triso insulation.How come, when there's equiv of a 70mm hole per m2 in it?
Posted By: Mike Georgemake a valid comparison is how big a diameter hole all of the air paths in flexible insulation are equal to.... (ie compared to your calculated 70mm hole)
No need - the point is that either is a hole quite big enough to fall into. You know, Mike, that 'airtight' isn't airtight until the very last crack sealed up - it's very steeply 'geared' - 'quite good' isn't any good at all.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227978#Comment_227978 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227978#Comment_227978 Fri, 31 Jul 2015 21:02:09 +0100 Mike George
What you are suggesting needs to be proved or disproved by the same calculation method.

Or alternatively a simple lab controlled blower test of each material (in isolation).

Either of these in a way which can be duplicated at will by anyone.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227980#Comment_227980 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227980#Comment_227980 Fri, 31 Jul 2015 21:57:41 +0100 djh Posted By: fostertomI once calc'd that those stitch holes are equiv to a 70mm diam hole per m2 of Triso.
Could you remind me of how that calculation worked, please?

Also note that a lot of little holes are different to a single big hole in fluid dynamics terms, so you need to know the flow rate (and fluid type and temperature etc) and run the appropriate equations to determine the equivalent size.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227982#Comment_227982 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227982#Comment_227982 Fri, 31 Jul 2015 22:33:31 +0100 Beau Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227984#Comment_227984 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227984#Comment_227984 Fri, 31 Jul 2015 23:32:31 +0100 mike7
Also there is the possibility - in my mind at least , not ever having seen a stitched multifoil - that the various layers are not pulled tightly together, but with a bit of distance remaining between each layer. That would create a series of orifices which IIRC has a rather greater resistance to airflow than a simple single orifice.

Edit:- Yep - if the distance between each layer is sufficient, the flow rate would be reduced by a factor of the sq root of the number of layers, ie 4 layers gets you half the leakage, nine layers one third, etc.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227986#Comment_227986 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227986#Comment_227986 Sat, 01 Aug 2015 00:09:33 +0100 ringi Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227988#Comment_227988 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227988#Comment_227988 Sat, 01 Aug 2015 01:20:05 +0100 Mike George Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227991#Comment_227991 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227991#Comment_227991 Sat, 01 Aug 2015 08:33:39 +0100 fostertom
It doesn't matter if it's a 70mm hole or a 700 or effectively just a 7 per m2 after fluid dynamics of small orifices, obstructions etc are taken into account - all are plenty enough to be serious breaches of any airtighness claim.

Posted By: mike7the possibility - in my mind at least , not ever having seen a stitched multifoil - that the various layers are not pulled tightly together, but with a bit of distance remaining between each layer
Yes, stitching was soon abandoned by the industry, in favour of spot-welding, giving both unbroken membranes and a lot less local compression of the layers - with that then yes it's worth bringing airtightness into the picture. But the Trisos, incl the ones in the notorious 'twin shacks' test, were far from airtight, so that can't justify any of the measured performance.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227994#Comment_227994 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227994#Comment_227994 Sat, 01 Aug 2015 10:00:10 +0100 Beau Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227995#Comment_227995 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227995#Comment_227995 Sat, 01 Aug 2015 10:44:22 +0100 SteamyTea Posted By: BeauIs it still worth counting the holes. Hoping you're going to say no
Yes, but you can do it over a small area.
May be worth cutting a bit open and post up a picture of it for us. I have no idea what it looks like.
Sounds like a bit of flexiable PU (foam rubber) between layers of metallised plastic film. If that is the case, can make your own pretty cheaply.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227997#Comment_227997 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227997#Comment_227997 Sat, 01 Aug 2015 15:27:28 +0100 fostertom
Easy -
how many stitch holes per 100mm;
x10 = per metre;
x how many rows of stitches (in both x and y direction) per m2
= total no of holes;
x estimated mm2 per hole
= mm2 open area per m2.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227998#Comment_227998 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227998#Comment_227998 Sat, 01 Aug 2015 16:00:20 +0100 Ed Davies
http://www.insulation-actis.com/produitsactis.php?p=3&l=3&rub=52&vert=3

Actis claim that Triso-super 10+ is “airtight” and has a water-vapour resistance of > 500 GN·s/kg (they actually write 500MN.s/g⁻¹ but we know what they mean). Might well be different from “9” product but if so it's interestingly different.

And no, you can't just add up the areas of lots of small holes to get the area of a single large hole. Well, you can, of course, but it won't have anything to do with the amount of air leakage. Air is viscous and the drag from the sides of all the little perforations is significant when they really are little. It'll be interesting to see how much it sucks.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227999#Comment_227999 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=227999#Comment_227999 Sat, 01 Aug 2015 16:44:41 +0100 fostertom Posted By: Ed DaviesWhy is radiant heat transfer considered “instant action”? OK, photons move pretty quickly but still it takes time for heat to move from one object to another with a similar order of magnitude rate as conduction. This was in answer to
Posted By: fostertomThat way, there would be great resistance to the instant-action radiant heat transfer across the void spaces,
leaving nearly all the heat transfer to be done by conduction via the circituous solid path between the bubbles,
and by convection across the voids.
As the latter two modes are subject to lag due to the thermal capacity of the solid, and the thermal capacity and the inertia of the air, their delivery of transfered heat is much delayed compared to the instant-action radiant heat transfer.
Consider an ideal extreme: a slab of 'solid' with lots of tiny irregular granular voids, a high void to solid ratio, so convoluted long-perimeter walls of solid between the voids. All is at static, equilibrium temp.

One face of the slab is suddenly raised in temperature, so a temperature wave-front starts propagating through the slab. The wave-front reaches the nearer wall of a void, so that wall suddenly becomes hotter than the far wall. What happens in response to that suddenly-arisen temp gradient between the near and the far wall of the void?

Yes, the temp wave-front will soon have passed on and beyond the far wall, and that void and its walls and immediate surroundings will be left equilibriated at a new, higher temp. But this is to look at what happens during the short time it takes for the temp wave-front to pass from the near wall to the far wall.

A temp wave-front advances because of heat transfer forward, driven by the suddenly-arisen temp gradient between the higher temp 'on' the wave-front (the near wall of the void), and the still-lower temp of the as-yet-undisturbed material beyond (the far wall of the void). As heat transfers forward, the 'beyond' material heats up and it in turn 'becomes' the temp wave-front, in turn facing yet more as-yet-undisturbed material beyond it.

Heat transfers forward, driven by the temp gradient; it heats up the far wall, so the temp gradient soon diminishes, the heat flow ceases across our void (but resumes, rolls on, further forward). This is to look at the short process by which that forward heat transfer suddenly begins and then tapers off to re-equilibriated zero.

Consider the far wall, which hasn't yet had any signal about what's coming to it. Suddenly the near wall is hotter than the far wall is. What is the first signal the far wall receives, in the form of a blast of heat? It's certainly not heat that begins to be transferred forward by means of conduction or convection - those will take a while to reach the far wall. The first signal that the far wall receives, is an instant (well, speed of light) blast of radiant heat, direct across the void.

That radiant blast, so early to be received, has plenty of time to heat up the far wall,
long before the conducted heat works its way along the convoluted long-path walls of solid between the voids, to reach the far wall, its propagation speed determined by the thermal capacity coefficient of the solid material;
and long before the convected heat crosses the void to the far wall, its advance speed limited similarly by the thermal capacity coefficient of the gas fill and by the inertial resistance of the gas-fill to buoyancy-driven bulk gas movement.

In fact the radiant heat blast may complete the re-equilibriation (equalisation) of temp between the near and the far wall long before the conducted heat and the convected heat get there; the temp differential may taper to zero so all three forms of heat transfer cease.

The point is, that the whole of the re-equilibriation (equalisation) may have been done and completed by radiant means, direct from near to far wall, by the time heat transfer finishes. The conductive and convective need not have bothered.

Note that this will only be the case during the one-off short time while the block of material is changing from one steady-state condition to another. Once that re-equilibriation is completed, the radiant transfer is no longer dominant. The radiant transfer performs the re-equilibriation and then settles back to its normal minor role, compared to conduction and convection.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228000#Comment_228000 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228000#Comment_228000 Sat, 01 Aug 2015 16:50:42 +0100 Mike George
From their BBA Certificate

9 Air leakage
9.1 When tested to BS EN 12114 : 2000 with positive pressure of 50 Pa, the products achieved a leakage rate of
0.19 m3·h–1·m–2.
9.2 When used as a vapour control layer and an air barrier, the products’ effectiveness is reliant on the careful
sealing of the laps, joints, perimeters and penetrations, in accordance with the Certificate holder’s instructions.
9.3 The airtightness of the building will also be dependent on the performance of the other building elements.

Available at http://www.just-insulation.com/006-downloads/WebDynamics/Certificates/BBA-WebDynamics-TLX-Silver-Roof.pdf

I have lots of other values for various multifoil properties if anyone wants to know.... I can only share the published ones though.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228002#Comment_228002 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228002#Comment_228002 Sat, 01 Aug 2015 17:02:16 +0100 Mike George
Air and vapour barriers
It is well known that as insulation improves the proportion of heat lost through air leakage increases, with as much as 40% being lost in this way As such, air tightness tests are now mandatory for a proportion of new builds and measured losses must not exceed 10m3/hrm2 @50Pa
The importance of GenX as an excellent air barrier should not be underestimated as the product BBA certifies an air leakage rate of 0.1m3/hrm2 @50Pa – a hundred times better than the whole building regulation requirement! This makes the product ideal for creating an extremely airtight envelope
Complementing it’s airtightness is a certified Vapour Resistance of 6000MNs/g, this rating as an effective vapour control layer.

Page 74 http://www.rcimag.co.uk/digitaledition/rci-oct-2012/#/74/]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228005#Comment_228005 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228005#Comment_228005 Sat, 01 Aug 2015 18:54:22 +0100 Ed Davies Posted By: fostertomThe point is, that the whole of the re-equilibriation (equalisation) may have been done and completed by radiant means, direct from near to far wall, by the time heat transfer finishes. The conductive and convective need not have bothered.I would think this needs calculations - intuition could be very misleading so I wouldn't want to even guess if this is right or not. Have you done, or seen, any?]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228007#Comment_228007 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228007#Comment_228007 Sat, 01 Aug 2015 19:31:30 +0100 fostertom
You're talking about a balance calc -

could (...) be done by the time (...) happens -
or not (not enough time) -
or not at all (fundamental insufficiency) -
or could it almost be done (significantly 'almost', or nowhere near)?

Could you help me, suggest the factors that would have to go into that calc?
For radiation I have emissivity of walls, speed of light.
For conduction I have conductivity and thermal capacity of solid, assumed path length thro the void's perimeter solid.
For convection I have conductivity and thermal capacity of gas fill plus its density (hence inertia).
Anything else?

Note that 'significantly almost' would be good enough to support the argument; on the other hand 'fundamental insufficiency' would shoot it down.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228008#Comment_228008 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228008#Comment_228008 Sat, 01 Aug 2015 19:35:21 +0100 fostertom Posted By: Mike Georgea certified Vapour Resistance of 6000MNs/gLike poythene then - not rocket science. Like polythene, all depends on the joint-taping.

The one time I had to justify this to Bldg Insp, the manuf got their tame boffin to calc the vapour resistance. He took the 6000 figure as resistivity and multiplied it by the thickness of the multifoil - 30mm! I was not impressed but the Bldg Insp was content.]]>