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freerangemonkey's avatar

What is the r-value of HDPE (high density polyethylene)?

Asked by freerangemonkey (348 points ) April 28th, 2008 from iPhone
Observing members: 0 Composing members: 0

8 Answers

PupnTaco's avatar

Great question for Google.

bulbatron9's avatar

Look on the packaging, or like Pup said Google it!

freerangemonkey's avatar

@PupnTaco: I am amused that you took more time to answer this with a googleit than to actually heed your own advice. Had you tried it yourself you would have found that there is not a readily available, obviously correct answer in the front page results for google. I know. I did try googling it. I got 4 different answers based on four different, not-entirely-apples-to-apples results, leaving me more confused than before.

I also tried: wikipedia, several engineering and chemistry related sites and my own library of engineering and building materials texts. How do you like them apples?

None of the sources I tried had a definitive answer. Trust me, if I post a question on fluther its because I want a fast answer…not to wait a day to get any answer. Obviously I tried googling it first.

If snarky, Ill-informed responses are going to become the norm here, I fear for the future of fluther as anything better than yahoo answers.
by the way… I eventually did track down what I think is the correct answer. I had to call a wholesale plastic supplier. He said he didn’t know the r-value, but gave me the thermal conductivity, k-value. A quick division into one for the inverse… 4.4/inch.

justeffinggoogleyourself.com

mvgolden's avatar

@freerangemonkey. R 4.4/in sounds high considering 3in fiberglass batt is R11 and 6in fiberglass batt is R30. Just my gut feeling.

freerangemonkey's avatar

It seemed high to me too. When you put it in those terms, it seems way out of whack. Especially considering it’s dense (thus the name!) so there is little air to act as a thermal break…

Back to the drawing board!

mvgolden's avatar

Have you looked at efunda

It’s got lots of great engineering data.

PupnTaco's avatar

I meant no offense; it seemed like an esoteric, technical question not many on Fluther would know. I assumed Google would have a quick answer – obviously I was wrong.

johnfurr's avatar

For anyone else that wants to know this answer… the correct answer and how to calculate if you ever need is as follows…

BTW @bulbatron9 never included the thermal conductivity he was told by the supplier, so we dont know if it was SI or Imp value… but it does not seem correct.

High density polyethylene is not commonly used for thermal insulation therefore you will not find published answers in r-value. However, engineering texts and plastics industry manuals list thermal conductivity is in the range from .46 to .52 W /( m-K ). This is a metric based SI value

You cannot convert a SI number into an imperial R-value by using the inverse as was stated by bulbatron9. It is an SI thermal conductivity value and not the imperial value…. we need to either invert to the RSI and convert that value to imperial R-value or convert the SI conductivity into imperial and then invert to determine the R-value.

To convert this SI unit to an imperial value we need to divide the SI thermal conductivity by the conversion factor of 1.7307, when we do this we find that the imperial thermal conductivity is .46/1.7307 = .26 to .52/1.7307 = .30 BTU / (hr-ft-°F).

Now we can calculate the inverse to determine the true r-value.

Thermal conductivity is the inverse of R value so now that we have the imperial conductivity we calculate the inverse 1/.26 = R 3.76 to 1/.30 = R 3.33

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