I want to make a overbag/quilt and I have the choice of Primaloft One and Climashield Apex. I can get both at 4oz/sq yd and at the same price.
The thing is, the Primaloft claims to be warmer at 0.027 CLO/g/m2 (vs 0.024 for the Climashield), but the Climashield is thicker at 2.5 cm (vs 1.8cm for the Primaloft).

This is counter intuitive: I would expect the thicker material to be warmer.
Is there a logical explanation for this, or could the retailer have their figures wrong?
Which would you choose and why?

I have a piece of each - 2.5 oz/yd2 Apex and 3 oz/yd2 One.

Curiously, the actual weight was 2.62 for Apex and 2.38 for One. I think this is just that the actual weight can vary from sample to sample.

Measured loft was 0.68 inch for Apex and 0.60 inch for One - so almost proportional to the actual weight.

I measured Clo/oz/yd2 at 0.81 for Apex and 0.91 for One - although this is a tricky measurement. The specs I found are 0.82 and 0.92, which is close to my measurement but different than yours? Regardless, I think that the One is a little better. Also, the Clo/inch is better for One. Just looking at the insulation, the One has finer fibers which must be why it has better clo/oz/yd2.

Downside - the One is much more fragile - tends to come apart more - again, why it has better clo/oz/yd2? So, Apex you only have to quilt around the perimeter, but One you have to quilt every 3 or 6 inches. Where you quilt it, the insulation is compressed so you lose some of the clo/oz/yd2 advantage. And all the extra quilting is a pain to do.

I've done a couple projects since I had that data and used Apex.

Loft isn't a good indicator of warmth between different insulators. Aerogel, CCF, thinsulate all insulate very well for their thickness. It all depends on the mechanism the insulator is using to keep you warm. The way it works out though is that usually the lightest techniques to insulate are less efficient on thickness (down, synthetics) but also are better suited for clothing because they're softer. All that really matters is warmth per weight for a given area for lightweight backpacking use.

PL1 wins on this front. They accomplish this by using much finer fibers in their insulation than the competition. The downside is those fibers are less durable and require stabilization (quilting) to keep the garment useful for longer. PL1 is also softer so it's favored for clothing over APEX.

So basically people will use APEX for large panel insulating (like a quilt) because you don't have to sew through it periodically. This eliminates cold spots. For small panels, like jackets, PL1 makes more sense because the quilting is minimal for a garment that already has a lot of seams, and the fabric drapes over the body better.

Thanks guys, apex it will be then, for ease of working with.

I've been building quilts, sleeping bags, and even a blanket using PrimaLoft One on a quilting rig that I built. If anyone is interested, I may be able to quilt a length of PrimaLoft One for you.

Do you have a picture of your quilting rig?

Yeah, but it's none too pretty. I've been developing it over the last year. Adding this, tweaking that. It's still rough, but it works pretty well.
I'd go into it more, but since it works - I've quilted about a dozen products with it - I won't be making improvements until I have have to.

I'm happy to do small jobs for free though, enough for a couple of bags/quilts at a time. The quilting goes pretty quick with the rig and my needle-feed sewing machine.

my understanding is the bigger difference between the two are softness and required quilting as mentioned.

not so much the warmth. the manuf. ratings are close. seems to me, when i have looked, that the given CLO rating for P1 is higher but then the weight of the material offered is slightly lower. i guess the manufacturer is saying P1 should be warmer so we are selling this slightly lighter weight that will then be as warm as the slightly heavier Apex... or, maybe i am mixed up.

i think P1 is supposed to be more compressible... i don't have any links at hand but that would be a thing to search for if it interests you.

In my experience, over the last 5 years of usage , PL1 does not retain it's loft as well as climashield xp over time (possibly due to difference in staple length/structure ).

I understand about loft not equal to clo due to differences instructure of material, but am sure my 'squashed' PL1 jacket is not as warm as when new. The climashield quilt seems to have fared better.

This maybe why MLD uses apex?

I wouldnt want to invest the cash and sweat and tears into making a PL1 quilt.

I'd maybe use PL sport if I couldnt get clim
ashield as it is more physically resilient than PL1.

Thru-hiker used to carry pl1 bonded to a scrim later to stabilize it. This eliminated the need to quilt it every 3”, but I think the clo/oz including the scrim was no better than apex.

Pl1 also drapes around you closer, and compresses much smaller than apex, but doesn't last nearly as long.

I think of apex as warmer, slightly lighter, and slightly more compressible than older synthetic insulation like polarguard 3d. I think of pl1 as a safer/moisture-proof version of 550 down, that only lasts a season or two, and is slightly less compressible, and slightly heavier.

Apex also lofts up significantly faster, and more fully, after being compressed in your pack all day.