View Full Version : A little of topic, insulation

Michael Az
07-30-2004, 08:43 PM
I know this isn't the Bob Villa home board, but I trust opinions that you folks here have a lot. A friend is building a new home and we are curious if this stuff is on the level or a scam. Maybe it would work in our shops also! It is called aluminum radiant barrier, very thin stuff, no fiberglass, no foam and sounds too good to be true. If any of you are contractors or have any experience with this please make a comment. This is on ebay and the fellow has a good feedback rating. Here is the link.
Thanks for any help.

07-30-2004, 09:01 PM
I did my own testing with mylar based radiant barriers and I can vouch for his results. That stuff is just downright amazing.

07-30-2004, 09:11 PM
Yes it is amazing and it does work,its also amazingly expensive.Its probibly one of those things that once you find the mfg it really costs $50 a roll instead of $5000

lotsa luck
07-30-2004, 09:22 PM
Having been in this biz... Works GREAT until oxidation sets in. Then the stuff sucks, big time, and is of little use. Some brands take longer than others but all will end up the same way. Put your money into other types that last.

07-30-2004, 09:36 PM
Aluminum radiant barrier. Expensive words for space blanket. Let's see- I purchased 36 sq ft of space blanket for 69 cents, how does that compare to ARB?
I also found something here called greenhouse foil. A little thicker but not more effective, also it was more munny. Less actual dollars that that roll on ebay, for the same quantity. And that was in canajun munny.

07-31-2004, 12:23 AM
I played with this stuff in the early 90's. It works great on radiated heat. But I asked about conducted and convected heat. They didn't want to hear about that. What happens when it gets dust on it in the attic, I've never seen a clean attic. That particular company also was pushing some sort of BS thermostat that had no readout or absolute adjustment knob. It just "knew" what to set the temp. on. It had a gold pad one could touch if they were uncomfortable and it would adjust itself. After a few questions I was not asked to come back or rep. their product! Being in the HVAC field for 20 years I've dealt with insulation and themostats a few times. If a shiny surface was an efficient isulation against heat then why does the meat I put on the grill wrapped in aluminum foil cook so evenly?

Spray on cellulose insulation is about the most cost effective and efficient insulation going today.


07-31-2004, 12:31 AM
Not scam. When insulating a ceiling lay down extra wide aluminum foil from the grocery store in the jumbo 200 ft roll. Put it on top of the vapor barrier and then put down the fiberglass. Cheap and gains about R3. It can also be put under roofing shingles at little extra cost. Same thing in walls.

07-31-2004, 01:29 AM
The stuff has virtually no effect on conducted or convected heat, only radiant heat (infrared). Shiny side down will keep most of the radiant heat in, and dust build-up on the top side won't affect it much. Shiny side up to keep solar heat out, and a dust build-up will a- absorb some of the heat before it gets to the foil, and b-interfere with the heat being rejected, keeping it close to the barrier, so it gets conducted through it. Standard fiberglass slows convection, has low conduction, and if it has a reflective layer, it also blocks radiation. So adding an additional radiant barrier might not have as much effect as you expect it to. Styrofoam virtually stops convection, but still has conduction, and I've never seen it come with a reflective layer, so in that case, the space blanket will make a significant improvement. I'm not sure about vermiculite and similar, it seems that these would reflect radiant heat to some extent, as well as reducing conducted and convected heat.

Why does food wrapped in foil cook, and so evenly? So much of the heat is conducted into the food that it cooks, and the foil conducts heat well, spreading it around the package evenly, reducing hot spots. Convection in the oven or barbeque brings a larger percentage of the heated air into contact with the food package, so more of the heat is transferred to the food. Increasing convection, as in convection ovens, improves this process. Radiant heat transfer may be blocked, but it's not the main method of heat transfer into the food.

Now consider what happens if the food wrapped in foil is placed in a vacuum. No air can touch the package, so only where the package is supported can heat be conducted in. In this case, radiant heat would be virtually the only heat getting at the food, and if blocked by foil, would then mean that you're going to eat cold potatoes. Nothing is perfect, so some heat would get through, but not enough to give you a hot meal today.

An interesting note is that foil has a shiny and a dull side. Which side should face the oven, and which should face the food?

Back to the radiant barrier, is that stuff like bubble pac? If so it slows convection and conduction, and blocks radiant heat. I can't imagine that just the thin mylar sheet can do a credible job of replacing regular insulations, even though it has a considerable effect on it's own.

[This message has been edited by darryl (edited 07-31-2004).]

07-31-2004, 01:38 AM
According to Reynolds, it makes virtually no difference.

07-31-2004, 02:40 AM
I used the Al foil in my attic. Considering the really minimal cost of doing so it doesn't have to be very effective to pay for itself. It also adds another layer of vapor barrier, a really good one. I suspect the best application would be under asphalt roofing shingles.

07-31-2004, 08:37 AM
Asphalt roof shingles,three profane words I don't care to utter,what a usless system,30 year warranty my a--.

I have seen several roof systems put down using either standing seam metal or industrial corragated in Galvalume where the stringers were placed up on a second layer of perlins laid down over the plywood skin,the advantage was the hot air in the summer would cause onvection and rise up and out the ridge vents drawing more cool air in from the drip edge cooling the roof.One house in question did this after having a black asphalt roof,their light bill in the summer dropped $40 a month,plus NOTHING sheds water like metal.

07-31-2004, 09:26 AM
As others have suggested: heavy-duty supermarket aluminum foil is a heck of a lot cheaper and I expect just as good a radiant heat barrier.

If you use something like this, I think you want some amount of air space in front of it -- if it's laid right up against a surface, the heat conducts right through it.

I think for a new house I'd go with the spray-on foam-in-place stuff that's been shown on "This Old House" a few times.

07-31-2004, 09:37 AM

I have heard of cyanide gas being produced from the BLUE foam insulation everyone was required to use at one time.

Seems the blue dye in electric wire has cyanide in it, as well as blue carpet. People were killed in France in a restruant fire making the most public display of what I am saying.

A sick house, one with enough chemicals in the air to make you sick all the time is no joke. One of our competitors in the chemical mixing industry in the 80s produced a machine that applied stainblocker with such disdain for the amount of acid and caustic that the carpet produced rotted the ceiling tiles out of the building they were in. I got to see this in person.

While building a house you need to consider all this.

Fiber from fiberglass if not sealed in the walls will cause lung damage to rival the asbestos of years ago. NOT PROVEN yet, but just wait a few more years. The dust hangs in the air while, wear a dust mask.

OUR powdercoat oven made with cerwool kept putting "dust" into the powercoat, as it would heat and expand it'd burp fiber into the oven's circulation fan.

ONE excellent insulation is the carpet fiber ground up and blowed into a attic, it has fire retardant on the carpet during production and before grinding up. A guy local here has became a millionair because of inventing the process.


07-31-2004, 10:56 AM
Thanks Darryl, You explained my thoughts on foil insulation better than I can.

I just hate to see folks throw money at something that doesn't work nearly as well as advertised.


07-31-2004, 11:26 AM

Asphalt shingles work well if you are in the right climate. I live in a very dry climate where the moss barely grows. The shingles on my roof are at least 30 years old and are just beginning to look like they need replacing. I will replace with a metal roof for fire safety reasons. However, I saw a show on TV from UL Labs about how they test this stuff for fire safety. They had a large chunk of wood burning away in a forced air draft equivalent to an 18 mph wind on an asphalt shingle roof. It burned for about half an hour without the roof catching on fire.

Michael Az
07-31-2004, 01:44 PM
Thanks for all the advise fellows. All the info is great and appreciated. For Lotsa Luck about the oxidation problem, I should have mentioned this in the first post that we live in the Az desert. Temps usually around 100 degrees in the summer and very dry. The humidity is usually less than 20 percent and I wonder if that factor wouldn't eleminate the oxidtion problem? The roofing on this house is metal with fiberglass under the metal. Thanks again

[This message has been edited by Michael Az (edited 07-31-2004).]

07-31-2004, 06:41 PM
Evan,down here in the heat they don't last long at all,I got some that are just 8 years old and are starting to fail,they will be replaced with galvalume R-panel.Seems like at the time we paid $42.00 a sq,top-o-the line Owens Corning fiber glass,replacement warranty says they will only pay for new shingles,I'm going to tell them I want a check http://bbs.homeshopmachinist.net//biggrin.gif

I already did two addition roofs with the R-panel in a med. grey color,the inside temperature difference was nearly 30* cooler for the metal over the shingles and I didn't even use the extra fir-ing strips.

07-31-2004, 07:07 PM
Yep, in our climate here it is more or less below freezing for about half the year. That is a great preservative for just about anything so you can double the life of whatever it is that is exposed to the weather. Except me. Of course the summers here are a different story. It is about 93° right now but the humidity is only 32%. It's a dry heat....