Edit: Missed a dot. Sorry.

sandshark wrote:kolm... when you said, "Of course it works", you were correct. And it's much more insulative than most materials.

Of course. Vacuum is even more insulative. Which does not make it the method of choice for insulation.

Let me remind you that plywood does NOT have a K value of .02.

Let me remind you that I wrote explicitly that it has a K of around .1, so it stands to reason that I actually know this.

Look, I calculated that 2.5cm of plywood should have better insulation than 3mm of this stuff. If there is an error in this derivation, please point it out, I do not want to baselessly talk down a product. Unless someone does, however, I stand by the claim that 2.5cm plywood are a more efficient insulation than 3mm magic paint.

Anyway, to your point... when is the last time you saw a pipeline coated with plywood to insulate it?

That's exactly the one and only potentially economically sensible application that I could come up with after some thinking, too. It depends a lot on how temperature-resistant and corrosion-resistant etc. the stuff turns out, but it could be some alternative for insulating pipelines, in particular for conditions where more cost-efficient solutions won't work.

'Could' being the operative word here. Lots of ifs attached to that one.

What about a home which was poorly insulated (yes, fiberglass is good but sometimes doesn't exist)? Can you just put plywood over top of any substrate and ruin the look? No, you can't.

Yes, I can and probably would, if that were the most efficient solution. (I realize that most people are less rational about cost/energy issues, of course, but that is not the point I investigated.) However, I would never, ever recommend to insulate with plywood if - as virtually always is the case - other alternatives are available; that was just an example of a low-tech insulation material that can still compete in cost efficiency.

Oh, and in case you did not notice: 2.5cm insulation with plywood is a joke for home insulation, not an insulation deserving its name. I live behind 8cm of plastic foam, and that's still not satisfying.

(Btw, there are houses in my village with less than 15kWh/m^2 per year (yes, per year, their heating bill for 100m^2 is about 200$ per year), which have >15cm fiber glass; that's serious insulation.)

But you're wrong about its efficiency being poor, so most of the argument you just made is errant. Your logic is good, but your premise is wrong.

We might talk about different things. I would say that it was not my premise but rather my conclusion that the efficiency, in terms of dollar per insulation value, is poor. Let us walk through step by step: We assume no drafts or radiation. Then the costs needed for heating with any given insulation with a certain material is given by the energy outflow through the insulator, which we found was

k/x *D,

where D is a constant independent of the insulation. Obviously, it would be optimal to set k/x to zero somehow. Cost restraints, however, come into play. I will make the simplified assumption that for each material there is a certain fixed cost C of dollars per cubic foot of material. Since the area is roughly fixed, this results in a cost of C/Area dollars per thickness of insulation. (For large quantities of material, this looks like a very reasonable assumption.)

So what would be a reasonable measure for cost-efficiency? Let us try and compare two available materials m1, m2 with t.c. k1, k2, and costs c1, c2 of dollars per foot of insulation material. It is reasonable to scale both such that the insulation is the same, i.e., we choose x1,x2 such that k1/x1 = k2/x2(*). The cost of insulation is then given by x1*c1 and x2*c2. When is material 1 more cost--efficient? Since both provide the same result, I'd say obviously this happens iff x1*c1 < x2*c2, which, due to (*), is equivalent to k1*c1 < k2*c2.

Thus, the quantity k*(cost/foot) (or, equivalently, k*cost/cubic foot) should be compared whenever you have two alternatives. [This is linear: If k*c is halved, the cost of insulation to a certain point is halved. OTOH, halving k while tripling c would be a poor trade-off.] I'm too lazy to do so now, but you are more than welcome to try and compare values with fiber glass or whatever. I would be very surprised if you get anything remotely as cost-efficient as standard materials can offer.

You are right that if one looks hard enough, one might find special applications where other, more cost-efficient materials are not available; also there are examples where other benefits outweigh a lack of cost-efficiency, but standard home insulation is, IMHO, hard to fit into that scheme.