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  1. #1
    stevebo's Avatar
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    insulation question..........

    Hey guys, just a quick question, with insulation, is it the amount of loft that matters, or the material used? In otherwords, if you have 2 inches of dead airspace, and 2 inches of insulation-down or what ever, which one is warmer, and why?
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    Senior Member TinaLouise's Avatar
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    Dead air space is cold. It's cold because there's nothing there to hold the heat coming off your body. If you put an "air" mat under you, you will be cold. If that mat has down (or some kind of insulation) in it, you will be warmer. The amount of warmth is directly related to how thick the insulation is. That's why winter quilts are thicker than summer ones.

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    The difference, if there were any, might be more subtle than someone would notice.

    Compliance is where I see a difference, down tends to lay lightly yet comply and fill up spaces around me as compared with synthetics which tend to be heavier and less compliant, often allowing for air space between me and the insulation.

    Subjectively I'd say there's a good news and good news aspect to how down compares, both are obviously highly efficient as insulation layers but down just lays so lightly against my skin that it tends not to make me feel overly warm. Isn't this what we would describe as comfort.

    I think most every time I've felt overly warm under a down quilt, I could honestly blame it on having too many clothing layers on.

    David

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    Needs more Hang time Catavarie's Avatar
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    Yes its is the amount of loft more so than the material, but the material is going to be a factor as well. Small fibers such as down trap the air and decrease air movement, so as your body heats the air in the insulation the warm air stays put. If you used a fiber that was larger and didn't pack as dense there would be more air movement and the air your body heats would just drift away and be replaced by more cold air, darn thermodynamics! /shakefist
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    Senior Member JCINMA's Avatar
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    To answer your question succinctly, the loft matters more.

    To delve further into the issue, there are three main factors when considering insulation: loft, efficiency, and weight.

    Loft concerns the thickness of your insulation, and the air trapped inside the insulation heats up using your body temperature (or a hot water bottle, heating pad, etc.). This creates a thermal shield around your body, constantly bolstered by your body heat and battered by the cold air outside this shield. Because of thermodynamics, you are always going to lose this battle, but the more loft there is, the longer you have before you start getting cold.

    Efficiency is a property of the material you use, and is generally referred to with an R-value (or with clothing, a CLO value). For example, a vacuum insulated panel has an R-value of about 50, while Thinsulate has an R-value of 5.75. This is a measure of insulative efficiency per inch of thickness.

    Finally, the weight (or density) of an insulation is also important. I prefer synthetic insulations for 3-season UQs and TQs because I get some extra wetness security and it still doesn't weigh very much. However, I think synthetics are too heavy for winter use, so I use a down UQ for the winter.

    I hope that more than answers your question. Choose an insulation based on the efficiency and the weight, and then select the right thickness for your expected temperature range.
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    BillyBob58's Avatar
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    Quote Originally Posted by stevebo View Post
    Hey guys, just a quick question, with insulation, is it the amount of loft that matters, or the material used? In otherwords, if you have 2 inches of dead airspace, and 2 inches of insulation-down or what ever, which one is warmer, and why?
    It is both, seems to me. Thicker- with the same material- is warmer. 2" of 800 FP down - at least with the same density- is warmer than 1". Probably close to proportional. 2" of 900 FP down is equally warm, but lighter.

    But, a 2" thickness of down is probably not warmer than 1" of High quality CCF. And plenty of folks have taken 5/8" OCF HH pads with a very thin ( 1/10" or less?) reflective space blanket into the 30s or even colder and done OK. A 1.5" down UQ is well over 2 times that thick, but will it really be warm enough into the 30s? Not for a lot of folks. Maybe adding the space blanket is not apples to apples, but still it does not increase the thickness hardly at all, and we are talking thickness vs material.

    One more example: I have found one layer of 2.5 oz/sq.yd. Climashield to be warm in an UQ into the 40s with no other warm layers. This had a rated loft of a measly 0.6"! Can you imagine trying to be warm in the 40s with a down UQ with only .6" loft? 1.5" OK, but not .6".

    So my take is: thicker is warmer if you are comparing the same insulation. With different materials, it gets more complicated. But even with the same materials, I'm not sure about different densities. For example, just enough 800 FP down ( say one oz) to completely fill up a chamber just enough to give say 2" loft. Compared to the same chamber filled with the same 800 FP down but, say, 2 oz or 3 oz. The loft will be the same max possible of 2". The thickness/loft is identical. Will they all be equal warmth? I don't know. ( but some one here probably does!)

    Oh BTW, the reason ( or so I've been told) that dead air is not warm for the thickness - like in an air mattress- is that it is not actually dead. When you move the mattress flexes and the air moves around. The cold air more distant to you replaces the warm air next to your skin. One purpose of the insulation is to trap the air in many small spaces that are resistant to moving. So some say anyway.
    Last edited by BillyBob58; 02-10-2012 at 20:10.
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