Reflective Foil vs fiberglass insulation
Reflective Foil vs fiberglass insulation
(OP)
Hi all,
I'm the facility engineer at a small hospital, and we have a project contractor wanting to substitue a product called "Astro-Foil" in 5/16" (R-15 according to the literature) thickness in lieu of 6" fiberglass (R19). The website here
http://www.astrofoil.net/index.html
comes across, to me at least, as something uh... less than scientific.
Assume for a moment that the R values are equal. I cannot find any articles re: UBC compliance or non-compliance for that matter regarding this "NASA developed" product. Pragmatically, while I am sure it does something, I am not convinced that it is (almost) equal to 6" of Fiberglass or about 4" of rigid Foam board.
It never gets below 80F here, so winters are not a problem. My biggest concern is compliance with IBC and IECC.
Any comments welcome.
Regards all.
Mitch
I'm the facility engineer at a small hospital, and we have a project contractor wanting to substitue a product called "Astro-Foil" in 5/16" (R-15 according to the literature) thickness in lieu of 6" fiberglass (R19). The website here
http://www.astrofoil.net/index.html
comes across, to me at least, as something uh... less than scientific.
Assume for a moment that the R values are equal. I cannot find any articles re: UBC compliance or non-compliance for that matter regarding this "NASA developed" product. Pragmatically, while I am sure it does something, I am not convinced that it is (almost) equal to 6" of Fiberglass or about 4" of rigid Foam board.
It never gets below 80F here, so winters are not a problem. My biggest concern is compliance with IBC and IECC.
Any comments welcome.
Regards all.
Mitch





RE: Reflective Foil vs fiberglass insulation
I THINK to get anywhere near the effective R-value they are claiming however, requires it to be installed with strip spacers to maintain an air space.
I know of a large project in a year round cooling environment where it was substituted without approval as a duct insulation, on ducts in an attic space. The contractor had to fly in a thermal imaging person at his expense, and his reports were giving a 3/8 type bubble wrap (foil both sides) an effectivenesses of R11 to 13.
I believe a lot of it had to do with a proper air space between the ducts and the wrap. So it was allowed to remain in lieu of the ductwrap that would have nominally been in the R6 to 8 range.
If I had to chose between the three insulations you mentioned, I would pay extra for the rigid foam. Better yet, blow in icynene foam in the attic on the underside of the roof pitch and seal the attic.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
Beware!
RE: Reflective Foil vs fiberglass insulation
ht
and scroll down to the bottom for a number of tests and science on these products. Snake oil.
RE: Reflective Foil vs fiberglass insulation
You can get FG or rigid insulation with a reflective vapor barrier that will work the same as the substituted product.
RE: Reflective Foil vs fiberglass insulation
It is more effective than a piece of poly and a couple air flim R values for heat flow down.
Presently going through an American Cold front, its mid 70s and low RH. Next hot sunny day I will try measuring the surface temperatures on both sides of the foil, in a place where it is the only insulation between plywood roof sheathing (below dark shingles) and a T-bar tile.
A radiant guy should recognize the merit of reflecting heat away.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
In between the wood 'nailers' is 1.5 inches of foam. It is not as good as the Blue Dow SM or the Pink foam. Probably R4 per inch as a maximum.
The gable attic walls in the photo are insulated on the inside with 1.5 inches of the same foam. The wall paint is somewhat reflective.
The attic is not vented. This is in a year round cooling environment, latitude 19.5 degrees North.
I do not have the air conditioning started up yet, but I believe this will be more effective than R19 fiber glass at the truss chords and an attic that is a solar collector and humidifier. I am putting my money where my mouth is, these are my apartments.
Fiber glass also makes an air filter. It easily allows superheated humid air through. Difficult to have an attic vapour barrier in the tropics.
During sunny days with the ambient in the upper 80s, the under side of the sloping roof and the atttic air were both approximately 1F warmer than the ambient. I will condition the attic void with a little air, but I think I am going to monitor how the two middle units do, condition one attic and not the other.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
At normal temperatures, the radiant emission can be at least comparable to the convective transfer, so a radiant barrier can provide a substantial reduction in heat loss.
TTFN
RE: Reflective Foil vs fiberglass insulation
since some contact between layers mus tbe present which would effectivelty reduce the effective overall R value they claim.
Nobody should consider this without evaluating technical documentation by a third party. Their socalled "technical" report is just more sales jargon.
BUYER BEWARE!
RE: Reflective Foil vs fiberglass insulation
If you read carefully, it does NOT claim that 5/16" of their stuff has an R15 or R19 rating. In fact, they don't seem to provide any conductivity or conductsnce figures at all.
BTW, playing games with the definitions of R-value, conductivity and conductance is one of the favorites of slime-bag snake-oil insulation makers.
Bottom line is that yes, in the right conditions there is a value to adding a radient barrier component to an insulation SYSTEM. Foil bubble wrap by itself does not and cannot provide the same R-value as traditional insulation materials.
Oh, if anyone is interested, the all-time champion slime-bag snake-oil sleeze insulation is:
http://www.supertherm.net/home.htm
RE: Reflective Foil vs fiberglass insulation
A quick descipition would be a series of air cylinders 3/8" diamter by 3/8 high" approximately 1/2" on centre. The rows are staggered.
There is a reflective foil on both sides.
It is the tail end of a cold front, I will measure some temperatures when it heats up a bit.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
Using "R" values and "equivalent performance" is misleading because regular batt, or rigid foam insulation is a conductance barrier, while the foil stuff is a radiant barrier, and the way the industry standard calculates R-value, it's based on "conductance and air temperature", and it does not measure "mean radiant temperature" as one of the factors, so that's where the foil stuff provides different performance compared to the standard mass insulation materials.
RE: Reflective Foil vs fiberglass insulation
So as a quick fix, I bought a 500 square foot roll of bubble wrap and installed it in a manner similar to 'lining joists'in about 50% of my ceiling. Made a big difference, never calculated if it was an effective R-value equal to 'two air films with heat flow down', but next hot sunny day will take some temperatures.
In cooling the majority of heat transfer through an attic has to be radiant.
I think my apartments with reflective white roofs with R6 foam and sealed attics will be more effective than a vented attic with R19. I won't have any superheated humid air short circuitting in as infiltration either.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
Some quick readings that I have not analyzed.
Partly Sunny, in the shade outside about 82F dry bulb and 72%RH
The underside of the roof sheathing on the southern slope of the roof is about 112.5 F, used a Raytech MiniTemp
Some truss spaces only have the 3/8 buuble wrap as insulation, installed in a manner similar to line floor joists for return ducts.
Surface temperature on the underside of the 3/8 foil bubble wrap on south side of attic, again with the Raytech is 80.5 F.
Some truss spaces still have the friction fit R19, with the 'kraft paper down' rammed in betweem them, so the surface temp of the kraft paper was about 79.5F a degree cooler again measured with the RayTech. Again under south side of attic.
I stuck a thermocuple probe up in the attic above the foil and the air temperature was 91.5F. The air temperature under the ceiling tiles was about 75.8F.
It was hard to get an accurate tile temperature under just the foil or just the R19 due to placements of the diffusers.
Likewise, I can't easily get to the top of the foil in the South part of my attic, can do it in the north side, but not the same radiant heat as the sheathing is only 101 there.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
"f you wanted to model or calculate it zekeman, I have half a roll of 3/8" bubble wrap
A quick descipition would be a series of air cylinders 3/8" diamter by 3/8 high" approximately 1/2" on centre. The rows are staggered."
----------------------------------------------------------
I need a detailed drawing and an analysis of the emmivity of the foil surface as a function of temperature. And then I can do it.
And, by the way if the stuff is so good, why doesn't the manufacturer get empirical data SUPPORT claims made. Maybe he can't.
However I will gladly take a stab at an analysis once you provide the data includig geometry, material, material thickness, etc if it so pleases you.
RE: Reflective Foil vs fiberglass insulation
I can take a picture and you can use some good engineering judgement. Poly air bubbles and metallized foil.
So I just posted some 'empirical temperatures'
112.5F wood is radiating at it, the air above is 91.5F and its surface temperature on the underside is 80.5F. Some R19 exposed to the same scenario is 79.5F on the underside. Am I gettin R7 plus 2 air films?
It makes a difference in my office and I have also seen ducts exposed to 80F dewpoints not sweat with it.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
It is can see the staggered bubble pattern, approximately 3/8" diameter, about 1/2" on centre and staggered rows.
it would appear to be air pockets in between the cylinders.
however these cyclinders are better described as disks, there are two disks then about 5/32" in height in series, not the 3/8" tall cylinders like I was guessing at before.
Metalized film is on the two sides, most likely aluminum
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
79.5-75.8=3.7
80.5-75.8 = 4.7
3.7/4.7=0.787
Could be some air short circuitting from the attic and throwing readings off. The underside surface temperatures was taken by an infrared, the air by a thermocouple. I will see what happens on a hotter day with the sun directly overhead. Too bad this thread did not start a couple months earlier. Will also see if that raytech gives readings besides 'point 0' or 'point 5' as well.
But, I have seen it be effective at keeping heat out, just not so sure at keeping heat in. The highest R-value they show on the Astrofoil site is for "heat flow down" implying an attic almost triple what they claim for heat flow up, implying an attic in winter. They also seem to be relying on air flilms in those values. So would I use it in lieu of Dow Sm under the pex tubing in a slab, No.
Some houses here use it in their attics on the under side of the roof pitch,in lieu of fibre glass at the truss chords. The temperatures are bearable in those attics around 100F, while those temperatures with the insulation at the truss chords could kill you. That 130F attic air is the third hottest thing in an attic and it loves to short circuit the fibre glass. At 100 or 130, that air here still has an 80 dewpoint. So ducts less likely to sweat when exposed to 130.
Before my office, I have only used it myself as a return duct insulation where I was tight for space going through trusses.
But I have seen supply ducts not sweat when it was used, I have seen it applied to horizontal runs of large condensate drains as well, and I read a thermal imager's report on it some years back.
Maybe a couple inches of foil backed fibre glass can be more effective than thicker layer without foil in a hot attic.
Anyways, if you spent some time on attic patrol in the summer, maybe you would not be so gung ho to get on the complete 'snake oil' band wagon. I am in a year round cooling environment and the OP sounds like he is in Samoa.
A northern climate, it is easy to have a sealed vapour barrier at the ceiling plane, it is difficult in the tropics to do this. You would have to apply poly to under side of trusses, then insulate beneath the poly, then drop a ceiling below, to get the vapour barrier on the warm side of the insulation.With insulation at the truss chords you cannot get a sealed vapour barrier above it. So the function of the vapour barrier is to keep moisture from diffusing into a colder builing cavity, but it also stops humid air from passing through. Stack effect pushes up on the ceiling plane in the winter, but pressure differentials or even inverted stackes will pull attic air down in the summer.
You could take what seems the best approach for hot humid climates and not vent the attics, seal them, and insulate them at the pitch of the roof. The concept of attic venting was to eliminate ice dams, however in a hot climate it is veiwed as flushing out the heat.
If you can do it on the exterior of the sheathing, you are better off than doing it on the underside of the sheathing. It eliminates having a solar collector on the top of your structure.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
79.5-75.8=3.7
80.5-75.8 = 4.7
3.7/4.7=0.787"
----------------------------------------------------------
I applaud you for doing this and respectfully submit that your numbers on R16 look off to me. Even if the temperature on the upper surface of the R16 were 110, the total drop to 75.8 would be about 35 deg. Since R16 is about 16 times the resistance of the air film which is 1 at most, I would have to say that at most the inside surface temp difference to the inside temp is about 1/16 of 35 deg which is about 2 degrees vs your 3.7. Also, this method of comparison depends on small differences and so needs very accurate data which cannot be obtained with IR readings. maybe TC readings on the surfaces would be more accurate.
May be that the IR readings (which depend on assumed emmisivity) are not right. Please correct me if you think otherwise. By the way, why don't you take upper surface temp readings to make the findings more meaningful.
RE: Reflective Foil vs fiberglass insulation
But the underside of R19 in one truss space and the bubble wrap in the next truss space were taken with the same thermometer, one degree difference against the same heat.
Below these two different insulations was an air space of a couple inches then a T-Bar tile.
Maybe the numbers appear off because you are only thinking conduction and convection, a typical heat loss appraoch when sizing a furnace. I would expect the top side of the R19 to be warmer than the air above it. A thermocouple measured the air at 91.5F. Was easy to stick a bead up to get that measurement.
Based on the underside insulation temperatures, the foil seems to be 78% as effective as the R19 friction fit. An error of a 1/2degree could be quite significant. Is the R19 truly R19 as installed who knows.
When I get some overhead sun, I will try again. But preliminary measurements are suggesting it is not snake oil when the goal is to keep heat out.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
----------------------------------------------------------
First off , I am fully aware of radiation and its effect on the total thermal process. In this case, the effect of the radiative component from the wood to the upper surface acts like it has an h= about 1 for the 110 degree temp and since the film between the 91.5 and the upper surface has an h about = 1. You had better rethink your statement about the upper surface being higher than the air above it. If that were true, you would have 91.5 degree air between two surfaces, each higher than 91.5, an impossibility for thermal equilibrium.
Accordingly, the simple one dimensional thermal model for the R16 case is a source(point 1) at 110 deg connected by a resistance of 1 (equiv radiation resistance for a black body) to the upper surface (point 3) and another source at 91.5 (point 2) connected by another (film) resistance, coincidentally also about =1, Now taking the upper sirface as a node point(3) you get another resistance = 16 for the R16 insulation to the lower surface node point 4 ; from node point 4 to the room ambient air = 78 (point 5) we have another film R=1, which completes the simple model.
From this, I get an upper surface temp of about 101 and a lower surface of about 79.3. Your measurements don't come close to this and I am wondering why.
RE: Reflective Foil vs fiberglass insulation
It looks like I made your case for the temps on both sides of the upper air being higher; but this violates thermal equilibrium and suggests that the 91.5 deg air is still being heated and doesn't represent an equilibrium state.
What do you think?
RE: Reflective Foil vs fiberglass insulation
But 'whatever' the R-value is, you could focus on the underside temperature.
I don't know the trade name of the bubble wrap I have left over so I can't say if it is Astrofoil or Reflectix etc.
The attic air temperature was taken perhaps "inches" above the top of the insulations, and the underside of the wood sheathing is "feet" above the insulation. The roof pitch is not high like in a Paston Effect, more like a 4:12, but air could stratify a bit none the less.
With sun over head, it is not unreasonable for the roof sheathing to be the hottest temperature in the attic, the top of the insulation being the second hottest part of an attic and then the attic air temperature in third place.
http:
Room air was measured as 75.8 up just below the tiles.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation
I measured the surface temperatures the under sides of the insulation, and then the air temperature (75.8) under the ciling tile, pehaps an inch below.
There was more on an air gap below the bubble wrap as it was arced up into the truss space where as the kraft paper of the R19 was more or less flush with the truss chords.
In another part of the attic just minutes ago,roughly a noon EST, top side of bubble wrap 98.5 , underside of bubble wrap 80.5, again with the raytech, air above the bubble wrap 86.7 with thermocouple.
Raytech seems to only give either 'point zero' or 'point 5' readings. Tired it on walls , books , myself. Always ".0" or ".5"
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Reflective Foil vs fiberglass insulation