Foil Insulation or Foil Bubble Insulation

foil bubble insulation Foil Insulation or Foil Bubble Insulation

I hear people ask about foil insulation a lot and the first thing I have to do is stop them and give an explanation about what insulation is.

Insulation, in the context of what you are going to stuff into your attic, is a material that slows down the transfer of heat. Its really that simple. Fiberglass insulation, cellulose insulation, spray foam insulation and even rock wool are ways to slow down the movement of heat. We either want to keep heat out or in. Insulation can do this.

What people refer to as foil insulation or reflective insulation, is not really insulation at all. It does not slow down the transfer of heat. There is no R-Factor to it.

What foil does best, when installed properly, is to REFLECT the heat away. There is no slowing involved. As a reflective surface, the idea is to create a radiant barrier in your attic that the infra-red rays cannot get past. You will have a barrier that stops heat from radiating into your home (hence where the name comes from).

Foil bubble insulation, whether it is Reflectix, ARMAFoil, RadiantGuard, Polarlum, Ecofoil,  or any other brand can actually qualify as insulation. Unlike the regular foil, it has bubble wrap sandwiched between the foil. This bubble wrap, whether a single layer or a double layer slows down the flow of heat. Admittedly, the R-Value of bubble wrap is not impressive, but it does end up being a thermal break. this being the case, you can argue the case of foil bubble being insulation.

The bottom line is that a radiant barrier attic needs both the foil to block the radiated heat and insulation to stop the flow of convective and conductive heat. That is the only way to ensure that you really are stopping the heat from getting into or out of your home.

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5 comments to Foil Insulation or Foil Bubble Insulation

  • Jay

    Some claim that stapling radiant barrier foil on to the roof rafters will heat up the roof shingles and void their warranty. Is it true?

  • There is no voiding of warranty that I have ever heard. i saw a test report once that showed how it can heat up the shingles by up to 8 degrees compared to a non-barriered roof. this is well within any shingle tolerance that it is not going to void any shingle warranty. I measured my old house and the shingles were hitting 168 degrees BEFORE the barrier. I never saw it go beyond 170 after the barrier, so I don’t know if it was because the sun was hotter on that day, or if it was the radiant barrier. Either way, the shingles were fine.

  • Col

    Hi have bought Aluminium METALLISED foil bubble wrap to insulate mu hut.

    It is single aluminium metallised film with a single bubble so I am assuming it only has one foil layer. Im not needing any more that a basic layer in my hut to prevent the freexing conditions inside over the winter so assume this will be fine to use.

    My question in how do I mount it. Do I put the foil on the outside (facing the wall) with the buble on the inside or do I fit it the other way round witht he buble on the out side and foil on the inside?

    Should i also fit a builders moister barrier sheeting and if so what side do I fit this on?


  • ok, a radiant barrier is NOT insulation. in the winter, insulation is always better to start with. radiant barriers are most effective at reflecting heat back outside in order to keep your house cool in the summer. That being said, they can help in the winter too, but not as much as a good layer of insulation will. always point the barrier in the direction that you want heat to reflect. In your case, you will want to reflect your heat back into the hut to keep you warm, so the foil should be pointed towards the center of your hut (bubble facing the wall and foil facing you). Most of the bubble foils are moisture barriers as well as radiant barriers (you dont need an additional barrier). the thing about having a moisture barrier is that there really does need to be a way for moisture to escape rather than condense inside the hut. You could do this by leaving a few gaps in order to let the moist air out. The bubble wrap doesn’t give you much insulation at all, so you are trying to make the most out of the reflective part.

  • Col

    Ahh… My shed suffers bady in the winder with the cold.

    The walls are all tong and grove and have supports which are 4mm deep giving me some space for an air gap if I fit the foil on top.

    Would I be better fitting the moisture barrier on all walls direct onto the tong and groove. Then filling the gap with loft insulation wool (im assuming I will need to shred it down to fit in the gap as most are arround 200mm deep at best)and then fit the bubble foil on top of that foil inside facing?

    Im also planning on sealing up gaps in the walls (at the joins with expanding foam and double galzing the single pain perspex with a second layer perspex which will have a 15mm air gap (going buy the current window frame size)…

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