Originally Posted by AYCE from Thru-Hiker.com Message Boards
Down is a loose insulation. The quality of the down and the density to which you stuff it all makes a difference, so you're better off sticking with inches of loft and a consistent way of stuffing your projects as a way to equate inches of loft to temperature.
The synthetics, though, are uniform. Clo is a measurement of the thermal resistance of a material. It's like R-Value, but specifically for apparel and gear.
If you didn't have clo values available, directly measuring loft isn't a bad idea. And even with clo values, if you're comparing two sample of the same insulation the one that's thicker is warmer.
Where you run into problems, though, is that a given thickness of one insulation might not keep you as warm as the same thickness of a different type of insulation. In other words, comparing inches of loft between insulations isn't a good comparison.
The way you work with clo values is that you multiply the basis weight of the insulation by the clo value. So for primaloft sport(clo is 0.74/oz), a 1.8 oz basis weight layer of primaloft sport would have a clo of 1.8 * 0.74 = 1.332
The whole point of clo numbers is that they are an objective, reproducible, and independent rating of the thermal properties of an insulation. Using clo numbers you can compare and contrast the thermal efficiency of insulations.
As a project uses more insulation, the impact of the performance/weight issue becomes more significant, and there are other factors besides clo values that can have a big impact on how gear functions.
Lets consider a case that zeros out the impact of other factors besides clo in an attempt to determine how much of a percentage difference in the performance of the insulation to affect a significant performance/weight change. Here's a concrete example of the impact of three insulations, 3D, XP, and Primaloft Sport, chosen because all things other than the clo value will be for all practical purposes equal, and because the project uses a modest amount of fabric (2 sq yds).
My Maxima Jacket pattern in size large uses almost exactly two square yards of insulation: 2.02 square yards.
If you use a 3 oz basis weight of XP and a 3 oz basis weight of 3D, the total clo for each case is as follows:
3D: 3 oz * .63 = 1.89
XP: 3 oz * .77 = 2.31
This is a 22% difference in the total clo of the jacket: (2.31 - 1.89)/1.89 * 100%. All other aspects of the construction would be more or less equal: both are continuous filament and would require the same amount of quilting (only at panel edges), and both jackets would be the same weight since the same basis weight of insulation was used (3 oz) and assuming you make the other parts of the jacket from identical materials. 22% is a pretty significant amount.
Compare this to the same case where a short staple insulation, Primaloft sport, is used instead of continuous filament in the same basis weight as before (3 oz)
Primaloft sport: 3 oz * .74 = 2.22 total clo. There isn't much difference between the total clo of the primaloft sport and the xp (4%), but there is a pretty significant difference between it and the 3D (17%).
In the case of primaloft sport, the official guidelines for stabilizing it call for unquilted areas to be an area of 2 square feet or less. For our example, the jacket, this requires three quilt lines: one across the back at the armpits, and one on each of the two sleeves. I have Maximas I use regularly made from primaloft sport and XP that were made specifically so that I could subjectively size up the two insulations use in apparel, all other things being equal. Three lines of quilting is quite modest, and I didn't notice any impact. I don't notice any difference in warmth of the two jackets which is what I would expect given that the clo numbers are about the same. This further supports the idea that for all practical purposes the methods of construction are the same, making a comparison on a clo to clo basis of the two jackets a reasonable thing to do.
I *did* notice, as I have before, that Primaloft sport is much softer and feels better in a jacket than the stiffer continuous filament insulations.
Lets look at it from a different angle to determine the weight impact of the three insulations for a given clo value, all other things assumed to be equal.
In a size Large of the maxima jacket, the weight of the jacket exclusive of the insulation is about seven ounces.
In working with synthetics the following clo-warmth chart will help:
total clo approx temp rating
6 single digits
If I wanted a jacket to be warm down around freezing, I'd need a total clo of about 3*.
For XP, this means I'd want to come up with 3/.77=3.9 ounces of insulation per square yard.
For 3D, this means I'd want 3/.63 = 4.8 oz of insulation per square yard
For Primaloft sport, I'd want 3 / .74 = 4 oz of insulation per square yard.
(* I realize that the approx temp chart is subjective as it is based on my own experience with synthetics. You can subjectively call total clo of 3 any temp you want, it won't affect the rest of the argument)
Given that there are about 2 square yards of insulation required for the project, this means that the insulation in the jacket would weigh:
XP: 2sq yds * 3.9oz/sq yd = 7.8 oz
3D: 2sq yds * 4.8 oz/sq yd = 9.6
Sport: 2sq yds* 4 oz/sq yd= 8 oz
Lets add the various insulation weights to the base weight of the jacket in size L to get the projected weight of the jacket with the different fills:
XP: 14.8 oz
3D: 16.6 oz
Sport: 15 oz
So by going with either a high efficiency continuous filament insulation or primaloft sport as compared to 3D you save 1.6 - 1.8 oz respectively .
Or, looking at it another way
A Maxima made from XP is 12% lighter than one made of 3D: (16.6 - 14.8)/14.8 * 100%
A Maxima made from Sport is 11% lighter than one made of 3D: (16.6 - 15)/15 * 100%
A Maxima made from XP is 1.4% lighter than one made from Sport: (15 - 14.8) /14.8 * 100%
In absolute terms, an 1.6-1.7 oz is not a huge amount of weight. I like to think of small weights like this in terms of something I value highly on the trail: snicker's bars (2.07 oz/bar). So in light of AYCE's Snickers Equivalency Factor , by going with XP or Sport instead of 3D I get what is essentially a weight free snicker's bar in every resupply. Delicious snickers- the original energy bar.
Is it enough of a difference to completely shun 3D, or to swap out all your 3D gear for something else? This is a personal choice that people have to determine for themselves. If all other things were equal, though, and I had decided that I wanted to use a continuous filament insulation in a new project, I can't imagine a scenario where I would choose 3D over XP unless I had a bunch of 3D laying around that I wanted to get rid of. And if that were the case, I'd probably make window quilts out of it rather than anything I would be carrying on my back. My situation though is the exception and not the rule: I have access to the gamut of materials, can write off the wholesale cost of materials as a business expense, and don't have to rearrange my life to knock out a gear project. Someone in a different situation might look at a 3D project like Jardine's synthetic quilt and realize that it's a really good value for the price, would take little time to make, and would leave them with some $50 to put to another use. There is little question in my mind that any shell/insulation/liner apparel piece is warmer and lighter than a fleece alternative.
My own rule of thumb for matching insulations with projects is that if the panels are small, such as with apparel, primaloft's strengths are maximized (absorbs very little water when wet, very soft, very consistent in basis weights as low as 1.8 oz) while its weaknesses are minimized (needs to be stabilized every 2 sq ft, insulation not as stable)
For large panel projects for reasonably cold temps, like a sleeping bag/quilt etc, continuous filament insulations' strengths are maximized (very stable- requires little quilting for large areas, fewer fiber migration issues don't require downproof shell, high basis weights more consistent) while its weaknesses are minimized (absorbs more water than primaloft, small basis weights not as consistent as small basis weights of primaloft, can feel kind of stiff).