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Old 09-26-2009, 07:25 AM
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Default 6# vs. 8# insulation

Does it really matter if you use 6# or 8# insulation board for a given thickness? My shopping often turns up 6#. I realize that mathematically the 8# is more insulative, but does that pan out -- would one actually notice a genuine difference in heat-up times? Should we restrict ourselves to 8# for the most part?

Is it actually mathematically linear? Are three inches of 8# exactly as insulative as four layers of 6# or does it not work that way?

[EDIT: When I started this thread, I myself was fairly new to high-temperature insulation and accidentally combined terminology used to describe the density of insulating blankets (#6 and #8) with references to insulating boards. The mistake does not obviate the question, but may lead to further confusion by other newbies. Good luck.]
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Last edited by kebwi; 09-27-2009 at 07:38 AM. Reason: Imprecise wording may lead to further confusion by newbies
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  #2  
Old 09-26-2009, 06:51 PM
MK1 MK1 is offline
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Default Re: 6# vs. 8# insulation

I can't tell you the exact r-values but the #s refer to lbs per cubic foot, density. The lighter stuff (6#) is probably higher in r-value than the 8 as it contains more dead-space.

Mark
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Old 09-26-2009, 10:37 PM
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Default Re: 6# vs. 8# insulation

I realize that 6# means six lbs / cuFt, but I don't think you're right about the intuition that lower density is more insulative. I had the exact same thought you had: more air, better insulation, but everything I have read and otherwise been told tells me otherwise, that 8# is a better insulator than 6#. I have no idea why that's the case, but I think that's what I've been told.

I remain confused on the issue.
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Old 09-26-2009, 11:10 PM
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Default Re: 6# vs. 8# insulation

Are they both the same thickness ?
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Old 09-26-2009, 11:13 PM
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Default Re: 6# vs. 8# insulation

Thickness has nothing to do with density. You can purchase blankets in 4#, 6#, and 8#, relatively independent of a variety of thicknesses ranging from 1/4" to 2". For a given thickness, I would imagine that one of the various densities is the best, but I'm not sure which. The higher density blankets are more expensive, but have higher thermal conductivies...which I think means they let more heat through...so that means they are a worse option while at the same time costing more. It doesn't make any sense to me. I wish someone would clarify the matter for us.
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Old 09-26-2009, 11:27 PM
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Default Re: 6# vs. 8# insulation

Thickness has everything to do with density because it is the volume part of the equation. The thicker the insulation of a given insulating material will increase the degree of insulation. But I agree with you that the denser a material is then the better it conducts and worse it insulates. Maybe the lighter weight blanket would be more likely to compress under weight and therefore reduce its thickness and consequently its insulation value.
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Old 09-26-2009, 11:45 PM
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Default Re: 6# vs. 8# insulation

The technical data does not mention the insulation values, only thermal conductivity, which is like the opposite of R values. The stuff is extremely fireproof with a rating about double the temps we fire to, so presumably the denser material would suit a higher temp application. I use vermiculite for insulation and have not had experience with blanket, but it sounds like the low density blanket would be better.
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Old 09-26-2009, 11:54 PM
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Default Re: 6# vs. 8# insulation

...which is odd since FB, which is targeted specifically at oven makers, sells 8# blanket instead of 4# or 6#. By the logic presented in this thread, 8# is the most expensive yet worst option of the three common densities available.

I still get the impression that most of the responses in this thread are speculative as opposed to truly knowledgable. I agree that less dense materials *seem* better since they have more air and I agree on the intuitive interpretation of the thermal conductivity specs, which are lower for 6# than 8#, but my original question remains unanswered:

Is there a *qualitative* difference or for our purposes are they functionally equivalent? Does anyone's oven *behave* differently for having been built with one or the other? That's the question I'm trying to get an answer to in this thread.

...I am also confused why FB sells 8# for the reasons stated in this post.
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Old 09-27-2009, 12:17 AM
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Default Re: 6# vs. 8# insulation

Ask James. He's the one who's presumably recommended #8. My guess is that it resists compression better.
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Old 09-27-2009, 08:23 AM
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Default Re: 6# vs. 8# insulation

Found this thread just in time, I am about to purchase some insulating blankets...

Pinging James....
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