Teardrops n Tiny Travel Trailers

Think again. (The article below is from a home building site, but the issues surrounding foil faced bubble insulation would apply to trailers as well.)


Here's an article from GreenBuildingAdvisor.com

An excerpt from the beginning of the article...

" Posted on Mar 21 2014 by Martin Holladay, GBA Advisor

Foil-faced bubble wrap is a thin product that comes in a roll. Its R-value is dismally low.

Most brands of foil-faced bubble wrap are only 3/8 inch thick or less, and have an R-value of only 1.0 or 1.1. Since the product often costs more per square foot than 1-inch thick rigid foam rated at R-5, why would anyone use bubble wrap as insulation?

The R-value of foil-faced bubble wrap is so low that it has few, if any, advantages over rigid foam. Of course, the product’s foil facing can be used as a radiant barrier — but if you want a radiant barrier, cheaper products are available. (The bubble wrap layer is unnecessary, since it adds cost to the material without adding any useful thermal performance.)

Exaggerated R-value claims

Since the main benefit from foil-faced bubble wrap is due to its radiant-barrier facing, the product is basically worthless unless it faces an air space. A decade ago, when I was the editor of Energy Design Update, I noticed that many manufacturers of foil-faced bubble wrap were promoting their products for use under concrete slabs on grade. In this application, the shiny foil is clearly not facing an air space, so the exaggerated R-value claims made by bubble-wrap manufacturers were particularly outrageous. My article exposing the bubble-wrap scammers appeared in the September 2003 issue of EDU."..... more on the link above.

Comes down to be a more or less useless product for insulation, or at best a more expensive radiant barrier than alternative radiant barriers.

I read the same article. This is an issue that's been around for a while. The manufacturers and their fans aren't paying attention to what is said in the article. Used alone, it isn't that insulative or reflective.

On the Yahoo Van Dweller forum I called out some insulation 'expert' about what he was saying. My stance was that it if was as insulative as he claimed it would make great 'clothing'. It should replace my fleece or Marmot down jackets. Not the case. He got his back up so I just dropped out of the discussion.

Fill the space with foam.

Tom

I have not yet read that entire article but the excerpts are not entirely well informed.

The best use of foil is as a radiant barrier. If applied in a roof space it can be very effective in reducing summer heat ingress, in which heat energy travels DOWN almost entirely as radiant energy. A layer of foil, facing an air space, is very effective at reducing this and has the added advantage of not suffering from "heat saturation" like bulk insulation. Interestingly the foil face can be facing up or down. As long as the airspace is there it has equal performance. In fact downward facing foil insulation is often preferable as it reduces the chance of dust build up on the reflective surface.

On the other hand, the article is right in that foil products often have poor "R" values when used to reduce winter heat loss from a building in which the energy is largely carried UP by convection of warmed air. Bulk/foam home insulation is vastly superior in winter.

The article criticises the use of foil under a concrete slab as "clearly having no airspace", but correctly installed the air space will be BELOW the foil, in the cavity above the ceiling. The space between the top of the foil and the concrete will be a layer of bulk insulation to provide good "winter" performance. The possible advantage of adding bubble wrap to foil, though admittedly adding little to thermal performance, is that it may make the material easier to handle and install as the foil it self is only a few microns thick and needs some sort of backing material.

The "R" system was designed largely as a measure of bulk insulation's ability to keep cold climate buildings warm in winter and so do not accurately reflect (pun intended) hot climate performance. Occasionally you will see two R values listed for an insulation system, for up / down (winter/summer) performance.

My teardrop roof, designed for a hot to mild climate has, from the top, aluminium sandwich panel/air space/foil insulation/foam insulation/ceiling. It has very good performance in hot sun and moderate protection on cool nights. Your needs may differ

A clothing analogy? On a hot day do you wear a wide brimmed hat or a woollen balaclava ? Reverse for cold climates.

And the best thermal performance to keep heat in? A vacuum flask with a foil surface facing a vacuum.... nice hot coffee all day.

michaelrsydney wrote:The article criticises the use of foil under a concrete slab as "clearly having no airspace", but correctly installed the air space will be BELOW the foil, in the cavity above the ceiling. The space between the top of the foil and the concrete will be a layer of bulk insulation to provide good "winter" performance. T

You have totally lost me on your critique on what GBA has to say about concrete slabs and reflective foils... The foil under the slab is 8 feet or more away from the ceiling you bring into the discussion. If we put the foil/bubbles on the ground and place the concrete on top there is no air space adjacent to the foil on the ground. No air space on either side of the reflective surface. RIMA, the Reflective Insulation Manufacturers Association states right on their website, under Myths, that a reflective surface under concrete does not work as there is no air space. As in your TD roof example the air space is a critical ingredient.


Agreed that reflective surfaces are better used in a hot climate than in a cold climate. Much research has been done by the CCHRC (Cold Climate Housing Research Center) in Alaska. They have come to that conclusion in there testing. Although some research indicates that a radiant barrier under foam/bulk insulation in a raised wood floor (with air space under the bulk/foam insulation and above the foil) performs several times better than the reversed layers in a ceiling.


My main reason for posting the topic and link is that I have seen foil faced bubbles used to insulate the curved space in a CT wall to roof transition; packed in with the result of no air space; = poor insulation value. Though perhaps it is better than nothing. I've also seen foil faced foam panels installed with no air space at the foil face. The extra cost paid for the foil is wasted if the builder believes it is better than non foil faced foam. I will admit that I have used foil faced polyiso panels without an air space on occasion. That was done for the greater insulation of the polyiso itself and not for the foil.

Another reason for the post is that I have thought for years that many distributors and sellers of foil/bubble materials make extravagant claims for the effectiveness of the products. Some outright lies are still out there and potential customers should have more facts at hand before spending their money.

MtnDon wrote:You have totally lost me on your critique on what GBA has to say about concrete slabs and reflective foils... The foil under the slab is 8 feet or more away from the ceiling you bring into the discussion.

Another reason for the post is that I have thought for years that many distributors and sellers of foil/bubble materials make extravagant claims for the effectiveness of the products. Some outright lies are still out there and potential customers should have more facts at hand before spending their money.

Ah, my apology, I had perhaps wrongly assumed that the use of foil was for an overhead concrete slab. A space under a flat concrete roof or similar can be very effectively insulated to reduce downward heat ingress by gluing a foil face foam sheet to the underside of the concrete, foil face down. Typically a suspended ceiling is then fitted below this, creating an still air space.

A concrete floor slab can certainly be insulated in a similar manner to reduce heat loss to an under floor cavity. However, I agree, foil as a sheet under an on-ground slab is worse than useless !

You are right, there are many extravagant claims made for insulation products. Typically in a warmer climate such as the one I live in the bulk insulation industry is most guilty of over stating their advantages. The fact is that foil insulation is extremely effective in the correct application. Granted however, the bubble material laminated to it is of highly questionable value.

Ah! I never thought of overhead concrete slabs. I was thinking residential construction and here in the SW USA concrete slabs on grade, are the norm for building virtually all residences and most commercial buildings are only one story as well. So the thought of raised concrete floors never occurred to me. I know of one concrete on grade slab that was poured over the reflective bubble wrap because the owner-builder believed the false hype of the seller. To make matters worse he installed radiant tubing in the floor for winter heat. A large amount of that goes into the earth.