Originally Posted by NoD~
I will live in my delusional, non-scientific world and say that, simply by temperature of the hood a minute after driving, tells me that it is working. Even cardboard has an R-value. If the R-value of both the cardboard and the bubble foil comes out to about 1, that's still double the resistance compared to air. With how little space you have to work, it's hard to find any material that will insulate beyond that.
Science will help you. [apologize for the length]
And yes you are correct in saying it can double the almost nil R value to nearly nil R value (an extra penny does not make a one penny man wealthy.) My initial and later responses is not an attack on your report, just adding prudent information.
-The R value of corrugated cardboard (shipping boxes) is slightly over R 2 per full Inch uncrushed.
-The R value of flat cardboard (paperstock) is approx R .75 per inch.
-The R value of the bubble foil stuff is slightly under R 1 uncrushed in this situation.
-The R value of open air vastly depends upon the environment, but the bubble foil R value is from the encased air in this environment.
If the insulation touches both the hood and any part of the engine bay, you lose the skin effect of the air space R value which almost negates any gains unless you have a large gap to fill with insulation.
This is only in a sealed environment with the heat going one direction (UP) through the material. Open air (DOWN/SIDES) or other conductive materials (metal, coolant/oil fluids) in other directions would significantly reduce these numbers, which are already almost nil to begin with. And the hood is still short circuited with its contact points (Latch, hinges, etc.)
The issue is not whether trying something out that costs basically nothing is worthwhile, the issue is whether we say it actually produces significant results: the answer is No, it is impossible. I'm all for experimentation and tinkering. I'd love to see you fill the engine bay nearly solid with spray foam but wouldn't advise it.
The best insulator approach is the prius method, or an approach of it.
And then we tackle the counter issues, like placing a highly flammable material in the engine bay,
Or the fact that the foil wrapped bubble in this case actually insulates the radiant heat from the sun heating the hood if you are trying to keep the engine bay warm while parked in the sun - yet again the gain is minimal.
We can discuss what would be the most optimal insulator in this environment and try to construct it and do some testing, but the same limitations unfortunately apply and the costs out weigh the benefits.
I'm experimenting with an electric water pump and while I could post and proclaim its benefits, at the end of the day, so far it is looking to be a wash when all factors are concerned, plus the cost - but I've still got some tricks yet to try.
I appreciate the sharing of personal experience and results, but we also must keep in mind that this web board is used to provide information for those seeking out FE gains. This thread was highly misleading (I doubt intentionally) and missing some relevant facts. As you said in the prior post, there really isn't much you can do in such a small space, and then you have to add in the other factors.
Hood Insulation = Not practical, nor provides any meaningful results in and of itself, but its inexpensive, can provide sound insulation, and one must be careful of additions to the engine bay environment.