Green Building Forum - Multifoil Insulation Mon, 25 May 2026 16:09:42 +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=228009#Comment_228009 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228009#Comment_228009 Sat, 01 Aug 2015 19:41:02 +0100 Mike George Posted By: fostertomLike poythene then - not rocket science. Like polythene, all depends on the joint-taping.


It certainly looks like polythene to me .... coated in something shiny - not sure what.. Rub it between your finger and thumb and the coating will come off.

No comments on the air infiltration values?]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228011#Comment_228011 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228011#Comment_228011 Sat, 01 Aug 2015 19:51:31 +0100 fostertom Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228013#Comment_228013 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228013#Comment_228013 Sat, 01 Aug 2015 20:45:02 +0100 Ed Davies
With small cells, can we ignore convection completely (though, perhaps, include conduction through the air or other gas)?

Don't need to worry about the speed of light - that can be considered “instant” for these purposes I'm sure. The questions are:

1) In the steady state, what proportion of the heat flow is due to conduction in the walls and what to radiation across the voids?

2) If there's a heat pulse, how much are these proportions skewed by the delay to conduction as a result of heating up the walls?]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228019#Comment_228019 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228019#Comment_228019 Sat, 01 Aug 2015 21:43:22 +0100 fostertom Posted By: Ed DaviesWith small cells, can we ignore convection completely (though, perhaps, include conduction through the air or other gas)?Yep
Posted By: Ed DaviesDon't need to worry about the speed of light
My little joke!
Posted By: Ed Davies1) In the steady state, what proportion of the heat flow is due to conduction in the walls and what to radiation across the voids?
Good
Posted By: Ed Davies2) If there's a heat pulse, how much are these proportions skewed by the delay to conduction as a result of heating up the walls?
Not exactly. Not the proportion, more like what is the absolute total of the radiant component that is transmitted and received, during the time it takes before the conductive component(s) even reach the other side - and is that absolute total enough to have reduced the temp differential to zero, or almost to zero, all by itself without contribution from the conductive waste-of-time.

There is a bit more 'instinctive' thought to offer, on objections that I'm expecting around process 2) - hare and tortoise come to mind!]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228021#Comment_228021 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228021#Comment_228021 Sat, 01 Aug 2015 22:00:12 +0100 Beau
4 The outer reinforced foil
3 Light open wading
2 Very thin foil
1 Spongy membrane

Make up is 43211211211234]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228024#Comment_228024 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228024#Comment_228024 Sun, 02 Aug 2015 00:02:56 +0100 djh Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228025#Comment_228025 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228025#Comment_228025 Sun, 02 Aug 2015 06:40:36 +0100 Beau Posted By: djhIs the labelling of the photo correct? It's just that 2 & 4 look like foil to me, rather than 1 & 4. I presume 'Very this foil' is very thin foil?

Sorry no. Some dodgy typing when I needed some sleep

Now corrected]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228032#Comment_228032 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228032#Comment_228032 Sun, 02 Aug 2015 10:01:07 +0100 fostertom Posted By: BeauThere is a line of stitching every 650mm across the rollIs that '650' correct? Not how I remember it - I seem to have thrown my samples of such things away. Anyway, it's 650 or whatever c/cs in both directions isn't it - a square grid?]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228033#Comment_228033 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228033#Comment_228033 Sun, 02 Aug 2015 10:11:28 +0100 fostertom Less 2 x threads = 0.004mm2
So ea hole open area = 0.438mm2
Holes @ 10mm c/cs = 43.8mm2 per m run of stitching
Lines of stitching @ 650c/cs in both direcxtions = 3.077 lines per m2
Total open area = 3.077 x 43.8 = 134.8mm2 per m2
Equiv to 13.1mm diam hole per m2.

So, sorry not 70mm diam but 13mm.
Is that significantly airtight? Even postulating reductions due to small-orifice, self-closing inner layers etc?]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228034#Comment_228034 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228034#Comment_228034 Sun, 02 Aug 2015 10:26:33 +0100 Ed Davies
>>> from math import pi, sqrt
>>> r = 0.75e-3/2
>>> holeArea = pi * r**2
>>> holeArea
4.4178646691106465e-07
>>> colsPerMetre = 1000/65
>>> rowsColsPerSqMetre = colsPerMetre * 2
>>> holeCount = 100 * rowsColsPerSqMetre
>>> totalArea = holeArea * holeCount
>>> equivRadius = sqrt(totalArea/pi)
>>> equivRadius * 2
0.041602514716892185

Still be interesting to know how this stuff sucks.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228036#Comment_228036 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228036#Comment_228036 Sun, 02 Aug 2015 11:26:52 +0100 fostertom Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228037#Comment_228037 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228037#Comment_228037 Sun, 02 Aug 2015 12:13:09 +0100 SteamyTea ]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228038#Comment_228038 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228038#Comment_228038 Sun, 02 Aug 2015 12:27:47 +0100 Beau Posted By: fostertom
Posted By: BeauThere is a line of stitching every 650mm across the roll
Is that '650' correct? Not how I remember it - I seem to have thrown my samples of such things away. Anyway, it's 650 or whatever c/cs in both directions isn't it - a square grid?

No not a square grid just one direction. Probably was along the length of the roll but the sample I have left is as short as it is wide.

Did the suck as you suggested before and yes its not hard to suck air in from the face but I doubt that air is coming in from the others side more likely just draws air through the face layer and is entering from the sides. As I mentioned back a page the layer labeled 1 seems to partly seal around the stitching hole.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228043#Comment_228043 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228043#Comment_228043 Sun, 02 Aug 2015 13:22:38 +0100 fostertom
Could you somehow clamp a small square of it, which you mouth would fully cover, with line of stitching across middle of it? Then when you suck, with your mouth covering all the holes on the face you can see, the air can only have come right through from the other face of the composite, not come in sideways.

All in the interest of Science!]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228044#Comment_228044 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228044#Comment_228044 Sun, 02 Aug 2015 13:24:53 +0100 SteamyTea You are just reminding me of loads of, what are now, unacceptable jokes and quips. :cool:

The 70's were such innocent times.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228046#Comment_228046 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228046#Comment_228046 Sun, 02 Aug 2015 14:23:40 +0100 skyewright Posted By: Beau2 Very thin foil
No idea about Triiso, but IIRC the equivalent layers in the multifoil that I've seen (YBS SuperQuilt) were what I'd call mylar foil.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228048#Comment_228048 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228048#Comment_228048 Sun, 02 Aug 2015 15:51:42 +0100 Beau Posted By: fostertomOK stitching is just one direction - it really stitching @ 650c/cs, or 65c/cs or what?

Could you somehow clamp a small square of it, which you mouth would fully cover, with line of stitching across middle of it? Then when you suck, with your mouth covering all the holes on the face you can see, the air can only have come right through from the other face of the composite, not come in sideways.

All in the interest of Science!

650 mm centres for the lines of stitching Tom. Will mess about later with the foil when my wife is out. Don't really want to explain myself sucking at a piece of old multifoil :bigsmile:]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228051#Comment_228051 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228051#Comment_228051 Sun, 02 Aug 2015 16:58:15 +0100 mike7 Posted By: Ed DaviesFWIW (ie, not much), if it's actually stitching rows and columns on 65 mm centres then I make the area equivalent to a hole 42 mm in diameter:

>>> from math import pi, sqrt
>>> r = 0.75e-3/2
>>> holeArea = pi * r**2
>>> holeArea
4.4178646691106465e-07
>>> colsPerMetre = 1000/65
>>> rowsColsPerSqMetre = colsPerMetre * 2
>>> holeCount = 100 * rowsColsPerSqMetre
>>> totalArea = holeArea * holeCount
>>> equivRadius = sqrt(totalArea/pi)
>>> equivRadius * 2
0.041602514716892185

Still be interesting to know how this stuff sucks.

Blimey, Ed! And to seventeen significant figures too!
I prefer the sum this way:
100 holes per 1m row, and 1000/65 rows per m gives 1530 holes per m2
Plus another 1530 for the columns makes a total of 3060 holes per m2
Diameter of single hole will be 0.75mm times the sq rt of 3060 (which is about 55) ie. 55x 0.75 = 41mm

Or... with the spacing of 650mm rather than 65mm, divide that answer by the sq rt of 10 to get 13mm
(I ate all the pi's)]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228052#Comment_228052 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228052#Comment_228052 Sun, 02 Aug 2015 17:38:17 +0100 bot de paille Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228053#Comment_228053 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228053#Comment_228053 Sun, 02 Aug 2015 17:48:57 +0100 fostertom Posted By: fostertomLess 2 x threads = 0.004mm2at least I did, just so some bugger wouldn't say Aha, but ....

Gd work Beau]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228054#Comment_228054 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228054#Comment_228054 Sun, 02 Aug 2015 17:51:54 +0100 bot de paille Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228056#Comment_228056 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228056#Comment_228056 Sun, 02 Aug 2015 18:28:32 +0100 mike7 Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228057#Comment_228057 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228057#Comment_228057 Sun, 02 Aug 2015 18:33:26 +0100 bot de paille Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228059#Comment_228059 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228059#Comment_228059 Sun, 02 Aug 2015 19:06:15 +0100 Ed Davies Posted By: mike7Blimey, Ed! And to seventeen significant figures too!Well, yeah, could've added an extra line to round the result which nobody else (except maybe Steamy) would have understood so thought it better to leave it out and round it myself.

Still don't believe the stitching is on 650 mm centres. That's like yay big; waving hands around rather than fingers.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228060#Comment_228060 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228060#Comment_228060 Sun, 02 Aug 2015 19:25:04 +0100 bot de paille Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228061#Comment_228061 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228061#Comment_228061 Sun, 02 Aug 2015 19:42:11 +0100 fostertom Posted By: bot de pailletheir product certificate claims 100 percent air barrierOf course - nothing special - like polythene - all depends on the jointing/detailing/tape, installation care and durability of same - that's where it falls down.

Posted By: bot de pailleI dont see how the thread is going to only take up one tenth of the hole area, I would calculate that the thread wil probably block at least 60 percent of the potential air leak.
Nah]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228063#Comment_228063 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228063#Comment_228063 Sun, 02 Aug 2015 20:17:15 +0100 mike7 Posted By: bot de pailleI dont see how the thread is going to only take up one tenth of the hole area, I would calculate that the thread wil probably block at least 60 percent of the potential air leak.

I was just using Beau's figure of 0.07mm for the thread. Have just been and measured some ordinary sewing thread (0.15mm) and button thread (0.25mm), both no doubt squashed a bit by the micrometer. Also some monofilament which was 0.25 mm, so Beau's figure looks suspiciously low - I wonder if it was 0.007in ? Suppose it is 0.25mm: That would be one third the dia of the needle hole, so one ninth the area. Times two for two threads and subtract leaves seven ninths. Sq rt of that is about 0.88 so equivalent dia would be 0.88 times 41.6 = about 36 mm, ignoring any change in the discharge coefficient.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228064#Comment_228064 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228064#Comment_228064 Sun, 02 Aug 2015 20:50:43 +0100 Beau
mike7. Yes I was surprised how thin the thread was and measured several times with slightly varying results but I stand by 0.07 mm

OK now for the suck test.

Not sure weather I have just done this just for your amusement or a genuine scientific experiment but I can say it is NOT airtight but taping the edges made big difference to speed of my possible suffocation. Interestingly I could not noticeably blow through it.]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228066#Comment_228066 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228066#Comment_228066 Sun, 02 Aug 2015 21:26:42 +0100 SteamyTea Posted By: BeauOK now for the suck test.

Not sure weather I have just done this just for your amusement or a genuine scientific experiment but I can say it is NOT airtight but taping the edges made big difference to speed of my possible suffocation. Interestingly I could not noticeably blow through it.

Smile, your on Candid Camera :bigsmile:]]> Multifoil Insulation https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228067#Comment_228067 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=125&Focus=228067#Comment_228067 Sun, 02 Aug 2015 21:32:53 +0100 Beau Posted By: SteamyTea
Posted By: BeauOK now for the suck test.

Not sure weather I have just done this just for your amusement or a genuine scientific experiment but I can say it is NOT airtight but taping the edges made big difference to speed of my possible suffocation. Interestingly I could not noticeably blow through it.


Smile, your on Candid Camerahttps:///newforum/extensions/Vanillacons/smilies/standard/bigsmile.gif" alt=":bigsmile:" title=":bigsmile:" >

Na I checked the room before carrying out such lunacy.]]>