Thermal efficiency between m90,silk and 7d

[William Zila]

Hey guys so I'm making another round of prototype quilts still trying to find how I want to make them for resell. And my question is a quilt with m90 and 2.5 ounce climashield weighs the same as a quilt with a 5mm silk inner shell and a 7d outer and cost is about the same. Is the heat loss from going to silk and 7d so much more then the duel m90 that the extra insulations effect is balanced? I'd assume that 7d is not far inferior to m90 but I know silk is. My non scientific assumption is that the inner shell is not as much of a thermal factor. So I would assume that going to a insulation clo of 4 over 2 would far outweigh the loss of clo from switching to silk/7d over duel m90. I wouldn't think that m90 has a clo of over 1 but I could be wrong. So in essence my question is a quilt with 5ounce climasheild apex and a 5mm silk inner and 7d outer will be warmer then a quilt with 2.5 climashield apex and m90 for the shell ?

[Michael Barber]

You are correct. If you think about it, you're adding 2.5ozsy of insulation. There is no possible way that 1.8ozsy of shell (.9 shell + .9 liner) could possibly make up that difference. If it could, we would use M90 as insulation instead of climashield. And obviously you are changing shell material, not removing it. Now how much difference? That I don't know.

[William Zila]

Thanks mike I'm just making sure I'm not crazy haha I have a way of having ideas that make no sense. I'm hoping Roger can chime in about actual thermal differnece as in how much clo you lose usig silk/7d compared to m90

[Walter Carrington]

m90, silk or 7d have have very little insulation value and it's about the same for all three. They add a little bit through adding an air layer. They do prevent loss of heat from wind. So, whichever gives the most wind resistance should be the warmest. Inside a bivy or good tent I don't think there'd be much difference.

Silk would be the least wind resistance. I'm not sure if 7d or m90 has the most wind resistance.

So, going with the lightest shell and putting the saved weight into insulation would be warmest. Durability, breathability and water resistance are also important, with silk coming in last on all three.

[Troy Ammons]

Figure roughly 3 yards of insulation, 6 yards of cloth for a long size.
3 inside and 3 outside.

The silk I bought weighs right at .5 oz.
M90 weighs 1.05 oz per yard.

The difference is 1.65 oz or even less if you quilt is smaller. I have yards of silk just sitting here. I was either going to do what you are talking about, or make a
momentum 55 shell and have interchangeable silk covered climashield inserts. Sort of like swappable insulation setup, or just build a 2.5 oz with a pocket to slip in another silk covered 2.5 oz or 5 oz layer etc.

I ended up just keeping it simple and doing both sides of my last quilt with M90.
It is a narrow summer quilt for a hammock and weighs 12.5 oz.

The benefit as I see it is M90 is more durable and both inside and outside are DWR.

[Bill Fornshell]

Hi,

The real difference is in the cost between the different shell material you are looking at. Silk is a whole lot cheaper to buy.

I used silk for several quits and a couple sleeping bags but I also use them inside a Pertex Quantum and Cuben Fiber BIvy that only weights 4 ounces.

[Ron Bell / MLD]

A quality material will keep you warmer and dryer.

How?

If the air permeability is too low then not enough sweat vapor will pass – not good- if it is too high then warm air will move through too fast and cold air will enter the other way too easy. This can be more pronounced on a thinner quilt intended for medium temps.

Quick Test:

It is easier for people to inhale than exhale!

That difference in pressure that you are able to generate in each direction can help evaluate the air permeability of many small weave DWR and non DWR fabrics. Fit average adults can inhale about 30-50% harder than they can exhale. My notes apply to a fit man.

Hold the fabric tight to your mouth. With tight pursed lips suck in air though the fabric. You can tell it is moving OK- not enough to breath easy or anything close to that but defiantly getting some air intake- you could stay alive for 5 – 10min (exhaling only through the nose) but it gets very tiring pretty fast. NOTE : DO not try this more than 10sec. DANGER.

With the same tight pursed lips try to blow through it outward. Harder than sucking it in. It is fairly hard but you can get feel a very very tiny bit moving through and the air volume in your cheeks decreasing but not so much that you can actually feel it on bare skin close to the other side. -If you are strong and focus a single burst then maybe a tiny bit of feeling on skin. You would pass out in under two min only trying to exhale through the material. NOTE : DO not try this more than 10sec. DANGER.

For me, this test correlates to about .5-.9 cc of air permeability (AP) – A good range for a quilt, windshirt or bivy top.

With a thin and overly breathable fabric and you can easily suck and blow though even easier than above described- like light weight silks.

Frankly, all the sub .7oz sq/yd 10d , 8d , 7d , and 5d material I've tried have fallen above this .9 cc AP – like silk- all overly breathable. A thick DWR plus heavy calendaring would bring down the air permeability on those weaves into the good range but the weight of that extra DWR would push it well over .7 oz/sq/yd.

An AP above 1.0 would be good in a double wall tent inner that you wanted to breath a lot but wold not not as good in a windshirt, bivy top or quilt shell.

I have tested an 8d – pictured- that was good and had OKish DWR but the weave was dense and it weighed .76oz sq/yd- I will also say the Montbell down vest I have is 7d and just about right in dwr and breathability – BUT it is a very dense 7D weave (maybe even a 7d X 10D vs a 7d X 7d) and for sure it is over .7oz sq/yd. The total weight has more to do with the weave density than only the size of the thread (denier) and a small d dense weave can weight more than a larger d low density weave.

Can’t blow or suck hardly any air at all – or none? It’s may be pretty close to waterproof and not much water vapor can get through either. I note this since we saw some former BPL posts on a 20d recently that had a waterproof rating around 1,000mm- that's waterproof! The DWR is so thick it can not breath well. There is a lot more to this particular story and it involves me sending thousands of $$$ in fabric back to a distributor since it was a non-breathable and essentially waterproof small weave DWR.

NOTE: This simple test is for DWR breathable fabrics – it far more complicated with waterproof /breathable WPB fabrics and this test will not work at all. Don’t even try it.

There are a lot of variables that factor in – too many to go into in this post- so take it with a grain of salt.

Try this test on all those three samples you have and I think you will see a clear difference.

I do have a very set AP number I know I like for a bivy and light quilt fabric based on feedback from many many night in the field and I can now use this simple test as a fast screen on a stack of materials to narrow it down for more accurate testing.

Here is a pic showing stack of about 50 different small denier fabrics from a recent round of AP , Strength and DWR testing I used to select our latest fabric- Endurance 10d X 10D – In the pics show a range from a 5d X 5d .6oz/sq yd to a 20d that is 1.05oz sq/yd. We could have bought any of them but chose the 10d X 10D Endurance with a 3xDWR at .74oz sq/yd.

Well, I'm not sure how useful this since most folks won't have many samples to use to get a good baseline. The Momentum 90 and 55 from thru-hiker does fall into this good range. If you would like a sample of the Endurance 10d x 10d we use just send an SASE to me. If you do this test over time you may get a feel for what works for you. It could be very use full in testing windshirts before buying since you would have a fav at home to use as a baseline.

The OP asked about Thermal Efficiency for a quilt. Of the three choices listed I think the the M90 is the clear winner based on the above info. I think that the air permeability has the most correlation to thermal efficiency in a sub 1.1oz material.

For any application you have to balance the various aspects. For a quilt top, if the choices were all below about 1.1oz – I would then select the best one based on these criteria- listed in order.

1: Air Permeability- must hit the sweet spot
2: DWR Quality- must be excellent and last a long time without a negative effect on #1
3: Strength – must be strong enough for the application
4: Weight – If it is strong enough and all the above factors are satisfied- then lighter is better

Other factors like appearance, softness, workability, price , etc would more individual type factors.

[William Zila]

Wow awesome post Ron that helped a ton. I think I'll go with silk inner and M90 outer for the increased durability wind resistance and lower price thanks everyone for the quick and helpful replies

[Brian Camprini]

Thank you Ron for taking a hit for us. Seriously, that's a good real world test.

I just checked out Feathered Friend's website for the first time in a while and was over loaded with the fabric choices. Can anyone comment on the differences in the Pertex products? Endurance LT vs UL? Shield EX vs XT? And how do those compare to NanoShield and eVent? Jeez my head hurts.

[Pilate de Guerre]

Ron,

What does "a 3xDWR" refer to? I don't think I've seen anyone else refer to a 'multiplier' regarding a DWR treatment.

[a b]

This air permeablity stuff is a very real phenomenon for me, though i definitey could not explain it like Ron!
I used a quilt made with Momentum 90 fabric, the MLD Spirit 30, for the A.T. this year.
I had used a WM ultralight for the PCT and CDT but imagined i might have moisture problems on the wetter east coast on the A.T. so i switched to the synthetic Spirit quilt.
I was pleasantly surprised to find that even when i wore wet clothes and put my wet feet into my Spirit quilt each night, they would be dry each morning as would the quilt itself.
The momentum 90 allows moisture to pass through the fabric driven by body heat.
The Climashield Apex insulation would not absorb the moisture so it simply went through to the outside.
This was a big difference from my down filled WM bag.
In the wet climates of Washington state and Montana I would wake up to a soggy bag and the nylon shell would be soaked.
I am a lifelong WM down bag user having both a zero degree Antelope and a 20 degree ultralight. They work flawlessly until the weather turns wet for more than 3 days without a chance to dry them out in the sun.
The huge advantage my Momentum 90 Spirit quilt had was i NEVER had to worry about drying it out in the sun. My body heat did the trick most nights and even while it was wet it never felt cold or clammy.
This is gonna sound wierd; You know when you go out of your shelter to take a leak at night in cool weather and you kinda dread that "cold shock" of getting back into your bag. Momentum 90 fabric does not produce that cold shock but nylon does.
i am not talking about the loft or temperature rating of the bag/quilt.
i am talking about the instance feeling before body heat has a chance to warm the dead air spaces of the insulation.
I have my WM bags and MLD quilt spread out on the floor right now and there is a very real difference between the way the nylon feels and the way the momentum 90 feels. The M90 feels instantly warm to the touch. The nylon feels cold until body heat warms it up.
I don't have the science to explain it, but there is a very real phenomenon going on here.

[Jerry Adams]

What about having DWR on inside layers?

It weighs a little extra

It inhibits breathability a little?

I wonder if inside layer improved breathability makes any difference? Maybe more water will get into the insulation layer but be less able to get out the external nylon layer?

Any MYOG they have for sale almost always has a DWR coating

[Ron Bell / MLD]

The 3x DWR refers to the coating process. Only a few high quality plants in the world can do this on the very small d fabrics. It's a three step treatment. It costs about $2 – $3 per yd more than a basic single dwr and can be 25% of the total cost.

On a production sample list of fabrics you will see the 3x options denoted vs the single pass types. There are other types too.

The 3x will last longer. You get what you pay for. Since we are a mfgr focused on top quality, it makes sense to make a bivy or quilt using only the best avaible since that is only $5 – $25 more in a finished product and it will perform better for longer , but we all know mamy are mainly competing on price alone .

[Ryan Smith]

Thanks for sharing Ron.

Ryan

[Pilate de Guerre]

Ron,

Thanks for answering my question and generally being so helpful and pioneering.

[Author]

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