Thin insulation

[mallymal]

UK "build in pipeline" member here!

Been looking at a material called DEPRON. I'm only aiming for a max 18mm thick cookie cutter wall (or even 12mm???) with a 6mm outer and 4mm inner bonded to it. So layering up this 6mm insulation could work well for either.

link is below...

Looks light, strong & cheap!

Anyone any experience of this stuff? And I'd appreciate the view of any experienced builders as to whether i'm sailing too close to the wind with a 12mm cookie cutter wall - trying to keep walls slim & weight down!

http://www.depronfoam.com

Thanks guys & gals

[grant whipp]

Hi, mallymall!

That DEPRON looks interesting ... might just have to contact the US distributor to get a sample! Looks to me, too, that it would work just fine. Wonder how the weight-per-square-foot compares to the 1/2" foamboard insulation from our big-box stores ...?

With regards to your proposed 12mm cookie-cutter'd walls, I don't see any problems there, either. To my way of figuring, 12mm is a close equivalent to our 1/2" (which over here is actually more like 15/32"), and that is what I use quite a bit of the time with 1/4" (6mm) plywood on both sides ... more than strong enough (and, as I've posted elsewhere, I save 100-150# over solid plywood, but still 50-75# heavier than stick-framed models).

Good Luck with your upcoming build! As always, then ...

CHEERS!

Grant

[vrooom3440]

The interesting thing about insulation is that there are two different mechanisms for heat transmission:

A) Convection - heat carried away by air movement or just molecular movement and what is handled by most insulation products. By inserting low density materials the molecular movement is greatly reduced.

B) Radiation - heat radiated away like light (think infrared) which is not really handled by many insulation products.

I got a better appreciation of radiated heat when I bought the tried a "space blanket". It felt like I could literally feel the heat being radiated back into my body.

I wonder about using the foil faced OSB from the big box store for flooring for example. The foil reflects radiated heat back.

Then there are the urethane foam panels with foil facing.

And finally the latest is the foil faced bubble wrap. This could work well with an otherwise structural wall.

The reflective types of insulation would be especially worthwhile in the roof of a TD. Reflect heat back out in summer and back in in winter.

[GPW]

Mally, we have much experience with Depron, using it to fabricate Electric RC Model Airplanes... It's fairly tough material for it's weight , and provides some degree of insulation depending on the thickness... It's nice to use, cuts easily, and glues with White carpenter glues or a hot-glue gun (carefully)...If you can obtain it for a reasonable price, I cannot see a reason Not to use it....
I can probably refer you to others in the area , who know where to get the best deal ....since you'll be buying a lot.. compared to us...

Common HD aluminum foil ,white glued to ply is an effective radiant barrier for our simple needs ...we use it for same in our Solar cookers...

[brian_bp]

The third mechanism for heat tranfer is conduction. Through solid materials, that's what is happening (gases conduct heat much less readily). Insulating foams reduce heat flow by interrupting the solid material with gaps of gas (bubbles), so mostly convection and radiant transfer are left; the small bubbles break up convective flow to reduce that mode within the insulation.

Reflective insulation only makes sense to me when the foil is facing a gap; otherwise, heat is transmitted by conduction (right through the foil) anyway, and there is no radiant heat transfer to stop with the reflective foil. In other words, if your wall or roof construction is a sandwich with no gaps, there's no point in foil; if there is a big space, then foil facing the space makes sense. In the foil-on-bubble-wrap stuff (such as Reflectix), if it is solidly sandwiched into a wall then the foil just helps a bit to reduce radiant transfer across the bubble spaces, which are poor insulators compared to a smaller-bubble foam.

The Depron stuff should be perfectly good insulation: extruded polystyrene foams typically have an insulating value (in old non-metric terms) of about R-5 per inch. Since we have half-inch extruded polystyrene available here, I would certainly use that rather than stacking two 6 mm sheets... but I suppose that you use what you can reasonably get.

[brian_bp]

That DEPRON looks interesting ... Wonder how the weight-per-square-foot compares to the 1/2" foamboard insulation from our big-box stores ...?

The Depron technical info web page quotes the density as 40 kg/m²; that makes no sense to me, because a one-metre-square sheet of 6mm foam would be nowhere near 40 kg - I assume that is was supposed to be 40 kg/m3, or about 2.5 lb/ft3; that would make 6 mm sheet about 240 g/m² (or about 1.5 lb for a 4'x8' sheet)... and on the very high end of the range of extruded polystyrene insulation board, at about twice as dense as the lightest stuff.

[mallymal]

Thanks for all the intersteing info guys - and thanks Grant for your reassurance re the 12mm cookie cutter wall (im certainly honoured to have one of the true teardop masters replying!!!!)

Will keep looking at diffwerent insulation. At our big box stores in the UK, the thinnest i've seen is 25mm (one inch), so that's why the Depron looked appealing.

Thanks again for great site & all the info generously shared

cheers

Mal

[Arne]

a space blanket will reflect your body heat but only if it is extremely close to your body. That is reflectivity.

If you put it into a t/d wall, you are dealing with conduction.. where it would be useless. Except as a vapor barrier.