MB Tachyon Anorak and layering

In my experience, Montbell stuff usually runs a little small. I can't say with any certainty, but if you're comfortable with an XL Houdini, I don't think you'll find the MB in XL to be too big.

Depends on what is your chest size.
I am 42.5", and can comfortably layer my Tachyon ('2013) size L over a baselayer and a fleece pullover.
No way could I wear it over a 1/2" thin down jacket without compressing the down. I have tried this just for grins with my Stoic Hadron cardigan jacket (perhaps a bit over 1/2" thick), and it does not work great.

I question why would you want to wear a windshirt over your insulation though. This is neither usual, nor provides any benefits. The insulation layer is made out of wind-resistant fabric anyway.

"I question why would you want to wear a windshirt over your insulation though. This is neither usual, nor provides any benefits. The insulation layer is made out of wind-resistant fabric anyway."

Hi Ivo,

I recall reading a thread by Richard Nisley in which he stated that adding a windshirt to a sewn-through insulation layer or fleece layer helped to retain some of its warmth. If I find the post, I will link it here.

Anecdotally, I have found this to be true and pretty awesome.

"…adding a windshirt to a sewn-through insulation layer or fleece layer helped to retain some of its warmth…"

@ Kelly:
I suspect what you are referring to is the chance of adding up to 0.6 clo to the overall clo score due to entrapped air. Valid only if the wearer is protected from wind dratfs.
In anticipation of you posting a link to Nisley's quote, and salivating over perceived benefit, I decided not to rely on recollections, so I just went and tried this ensemble again.
T-shirt, 100-weight fleece, Stoic Hadron (ok, its loft is perhaps closer to 5/8"), and the Tachyon on top.
I looked like the Michelin man – not so much in the torso, where some minor down compression was observed, but definitely in the arms. This picture refreshed my memory as to why I have decided the Tachyon should not be used in this fashion.

To sum it up, if your chest size is over 41", and your arms are proportionally thick, you better aim for the Tachyon in XL size.

Here you go Ivo:

Richard’s post at 15:32

“The secret to maximizing the efficiency of sewn through baffle garments, such as the Infinity or Helios, is to size either your wind shirt or hard shell to wear over it. The v shaped spaces between the baffle seams and the outer material of a wind shirt or hard shell create insulating air gaps that offset the loss of insulation at the seam.”

Thanks,Kelly.

Just what I thought.
Elsewhere Richard mentions this in more detail, suggesting that it might add around 0.3 clo to the ensemble, and could go up to 0.6 clo.

Unfortunately, This is not quantified. And here's the bad news:
It is only valid if the wearer is sheltered from the wind.

If I'm in my shelter, I can use my sleeping bag or quilt, and don't need this unquantified clo "boost".
If I'm outside, I might get the boost on the lee side, but not on the windward side, where the light shell garment would "mold" itself to the actual external profile of the down garment's shell, which would negate the insulative effect of the entrapped air layer in between. Besides, this would mean I'd lose body heat while removing my windshirt, donning the down jacket, and pulling the shirt over…. Nah, I'd pass.

To simplify, this borders black magic, as the user is never guaranteed to extract real benefits, and is not worth trying. Thus my windshirt never goes on top of an insulative garment.

On the other hand, I often do this layering using my (much sturdier, thicker, and less flexible) rain shell over my Hadron cardigan (sewn-thru), and am willing to bet that it does add warmth.

Of course, you HYOH.

My tachyon L is quite large, i have 42" chest and could easily probably wear M based on how roomy it is. Mine is newer model that weighs 1.9 oz or so, the older was 2.X.

Of course i also have 31" waist, that makes a difference too.

It fits well over my L exlight, no compression of loft. Like it was made to or something.

It also adds measurable warmth. My real world experience FWIW.

@ M B:

Perhaps Montbell have changed the cut on the new ones. My waist size is pretty close, measures 32".

How's the fit over the arms of your extralight? Any loft compression?

@Ivo
where do you find that adding 0,3 to 0,6 to the clo is only valid if sheltered from the wind ?

Ivo,

You said in part, "Elsewhere Richard mentions this in more detail, suggesting that it might add around 0.3 clo to the ensemble, and could go up to 0.6 clo… Unfortunately, This is not quantified. And here's the bad news: It is only valid if the wearer is sheltered from the wind… To simplify, this borders black magic, as the user is never guaranteed to extract real benefits, and is not worth trying. Thus my windshirt never goes on top of an insulative garment… On the other hand, I often do this layering using my (much sturdier, thicker, and less flexible) rain shell over my Hadron cardigan (sewn-thru), and am willing to bet that it does add warmt"

I will use the term wind shirt to mean wind shirt or hard shell since the test results are identical using either shell type. I will provide you with a set of my lab results that are the most similar to the configuration you have. The Mountain Hardwear Ghost Whisperer Hoody has an Iclo of .988. If a poor fitting (tight) windshirt is placed over it, it has an Iclo of 1.386. Tight fitting is defined by me to be a 0” gap between the outer insulation layer and the windshirt except for the seam depressions. This results in a 29% improvement (.4 Iclo) in the insulation value independent of the wind speed. If the windshirt was ideally fit, to provide an approximate .5” average internal gap, then it would add a ~.6 clo value independent of the wind speed.

There is also a surface boundary layer of approximately .6 clo maximum on the outside of the windshirt. Obviously this value does vary with the wind speed. Iclo + boundary layer is typically called the clo value. The "wind chill" temperature value is correlated with this ephemeral outermost air layer.

Radiometric Image of MH Ghost Whisper:

Radiometric Image of MH Ghost Whisper + Tight Fitting Shell:

"where do you find that adding 0,3 to 0,6 to the clo is only valid if sheltered from the wind ?"

@ Woubeir:

Here:

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=55696

Check Richard's reply @ 11/10/2011 21:32:51, where he says:
"…If you are sheltered from the wind, you can include a boundary layer of .6 clo…"

And then further, @ 11/11/2011 20:22:38:
"The boundary layer applies to any ensemble, if you are sheltered from the wind."

@ Richard:

Thank you for the explanation.

Your post here clarifies the nature of the surface boundary layer which adds up to ~.6 clo, as being a layer of air outside of the outermost garment.

It seems that I have misinterpreted previous postings of yours on the subject, assuming that this boundary layer is of air entrapped between the garments.
I now stand corrected.

As to the boost in clo of (1.386 – 0.988), of which you posted measurements here, my understanding is that it is due to the very windshirt on top of the down jacket, plus any air entrapped in between. I accept this, but wonder what would this boost look like if the shirt was blown by a strong wind over the jacket to the extent that its fabric is in full contact with the outermost fabric of the jacket, and entirely follows the topology of the jacket's surface. Which to me is a reasonable assumption in conditions of a steady 25 mph wind.
How about that? Can you simulate and measure this in your lab, or could you make reasonable assumptions of its impact on the clo boost?

Edited to add:
I always assumed (right or wrong) that the latest scenario I described above is equal to the scenario where the windshirt is worn under the down jacket.

Ivo,

You said in part, "what would this boost look like if the shirt was blown by a strong wind over the jacket to the extent that its fabric is in full contact with the outermost fabric of the jacket, and entirely follows the topology of the jacket's surface. Which to me is a reasonable assumption in conditions of a steady 25 mph wind. How about that? Can you simulate and measure this in your lab, or could you make reasonable assumptions of its impact on the clo boost?"

The structure of your down jacket, under your wind shirt, acts like a support structure for the sewn through seam's air gaps. I have a secondary research report, -filed someplace?- (my information posted above is all primary) that studied the optimal garment layer spacing for different wind speed ranges. In summary, it stated that the optimal spacing between layers is reduced slightly as the wind speed increases. It never went below .25" and I used 0" to illustrate a minimum 29% insulation improvement in your ensemble.

Richard,

Well, let's try to understand all of this, as its value may be quite high for current and future members of BPL.

When you mention secondary research, that means it is only of an interpretative character to explain or draw probable (sic!) conclusions from primary reports.
I dislike those, and many do not trust them – unless the author(s) has high credibility, and demosntrate(s) a verifiable train of thought.
Was that the case with the one you mention?

Then, you say that the average spacing between windshirt and the bottom of the "valleys" "never went below 0.25". What does this mean exactly? I am sure you fully realize that – depending on the topology of a particular sewn-thru down garment it may look like this

or like this

or perhaps like this – for a full "shrink wrap" effect, at high wind speed

Would you please, explain where is this zone of "never under 0.25" that you described – is it really the average spacing, or it is between the lowest "valleys" of windshirt and jacket in the second or the first picture, or it is the mean height of (perceived) air gap between the garments?
I ask because these are assumptions we all must understand, if we are to rely upon them.

The other statement of yours that you "used 0" to illustrate a minimum of 29% insulation improvement" in my ensemble leaves me quite puzzled.
You tested a Mountain Hardwear Ghost Whisperer Hoody, which has horizontal baffles, while "my ensemble" involves the Stoic Hadron cardigan, with square baffles, which would certainly define a different topology of the contact between windshirt and down jacket. Thus, the support for the windshirt, exerted by the "peaks" of the down garment, would result in different amount of sag at different wind speeds, and I have no clue where your "no less than 0.25"" figure would look like in that case.
Besides, from the second photo in your post, I judge that the "shrink wrap" effect is not there at all – how can you claim 0" of gap then?

I would be more than happy to accept your previous conclusion of at least 29% clo boost as it would greatly benefit me (and others), but at this point it just does not make enough sense to me. Please, elaborate.

Common sense and research data show windshirt should go over down insulation layer for optimal warmth. Why? Science.

Ivo,

You said in part, “When you mention secondary research, that means it is only of an interpretative character to explain or draw probable (sic!) conclusions from primary reports. I dislike those, and many do not trust them – unless the author(s) has high credibility, and demosntrate(s) a verifiable train of thought. Was that the case with the one you mention?”

By secondary research I meant peer reviewed scientific journal articles not authored by me and specifically citations 1-8 which I have studied and have in my possession. You can typically acquire any journal article abstract free and the actual article, to read but not publish, for $35 – $45 each. The following all reach similar conclusions to what I previously presented in this thread. I have not read any that supports your contrary position but, please post the citation if you can find one:

1-McCullough, E. A., Jones, B. W., and Huck, J., A Comprehensive Data Base for Estimating Clothing Insulation, ASHRAE Trans. 91, 29-47 (1985).
2- Havenith, G., Heus, R., and Lotens, W. A., Resultant Clothing Insulation: A Function of Body Movement, Posture, Wind, Clothing Fit and Ensemble Thickness, Ergonomics 33 (1), 67-84 (1990).
3- Y.S. Chen, J. Fan, X. Qian and W. Zhang, Effect of Garment Fit on Thermal Insulation and Evaporative Resistance, Textile Research Journal 2004; 74; 742
4 – Chris M. J. Sawcyn and David A. Torvi, Improving Heat Transfer Models of Air Gaps in Bench Top Tests of Thermal Protective Fabrics, Textile Research Journal 2009; 79; 632
5 – Guowen Song, Clothing Air Gap Layers and Thermal Protective Performance in Single Layer Garments, Journal of Industrial Textiles 2007; 36; 193
6 – B. Lee, Theoretical Prediction and Measurement of the Fabric Surface Apparent Temperature in a Simulated Man/Fabric/Environment System, Combatant Protection and Nutrition Branch Aeronautical and Maritime Research Laboratory
7 – Zhu Fanglong and Zhang Weiyuan, Measuring the Thermal Conductive Property of Protective Fabrics to Radiant Heat Exposure, Journal of Industrial Textiles 2007; 37; 175
8 – N. Mao and S.J. Russell, The Thermal Insulation Properties of Spacer Fabrics with a Mechanically Integrated Wool Fiber, Textile Research Journal 2007; 77; 914

The information I previously paraphrased from memory recollection literally states, “Under no wind, the thermal insulation reaches a maximum when the air gap is about 1 cm (.394 inches) thick, corresponding to a difference of 7.5 cm (2.95 inches) in girth between the garment and the body. Under windy conditions, the thermal insulation reaches a maximum when the air gap is about 0.6 cm (.236 inches) thick, corresponding to a difference of 5 cm (1.969 inches) in girth between the garment and the body.”

You said in part, “Then, you say that the average spacing between windshirt and the bottom of the "valleys" "never went below 0.25". What does this mean exactly?”

It means – from one of the secondary research articles listed above – Under windy conditions the thermal insulation reaches a maximum when the air gap is about .6 cm (.236 inches incorrectly recalled from memory as ~.250 inches) thick, corresponding to a difference of 5 cm (1.969) inches in girth between the garment and the body.

You said in part, “You tested a Mountain Hardwear Ghost Whisperer Hoody, which has horizontal baffles, while "my ensemble" involves the Stoic Hadron cardigan, with square baffles, which would certainly define a different topology of the contact between windshirt and down jacket. Thus, the support for the windshirt, exerted by the "peaks" of the down garment, would result in different amount of sag at different wind speeds”.

I used the Ghost Whisperer Hoody example because it was my closest equivalent product test result to your Hadron. The MB EX Light jacket has a square baffle topology and my comparable test showed a 29% difference in insulation value. The MB EX Light Anorak has a square baffle topology and my comparable test showed a 28% difference in insulation value.

You said in part, "The other statement of yours that you "used 0" to illustrate a minimum of 29% insulation improvement" in my ensemble leaves me quite puzzled." I meant both 0 inches spacing and/or girth increase between the wind shirt and the insulation. This was in contrast to the .239 inches of gap space or 1.969 inches girth increase, as mentioned above, for windy conditions.

The wind may push against an air gap augmented ensemble from one direction strong enough for a localized depression or collapse but, not continually from all directions at the same time. All of the air gap augmented ensemble's other sides continue to provide incremental insulation.

Richard,

Thank you again for the patient explanation.

I think I grasped all points you made, especially once you introduced the term "girth".

I was a bit unclear regarding where is the air gap measured – I now understand it is at the "peaks" of the lofted down garment (see my crude mouse-sketched pictures above), and not at the "valeys" as I assumed previously.

The only remaining unclarity is the relationship between air gap and girth.
You said, in part,
"air gap is about 1 cm thick, corresponding to a difference of 7.5 cm in girth between the garment and the body",
and,
"air gap is about 0.6 cm thick, corresponding to a difference of 5 cm in girth between the garment and the body"
In both of these statements, the air gap as mentioned is not between an external "shell-type" garment and an insulative garment, but precisely between a "body" (which I take to mean a manikin serving as a heat source, simulating a human body) and an insulative garment of a specific thickness.
If they meant the former, the girth "delta" would have never exceed a value of

(pi) x 2 x (air gap),

which is clearly not the case here.

If you can forgive me that I have not yer read the reference materials you listed, perhaps you could share whether the quotes I used above are still relevant (and whether are their values applicable) to the case in point, or – alternatively – a visitor to this thread should simply ignore them.

Ivo,

Yes one of the studies used your latter case definition, "I take to mean a manikin serving as a heat source, simulating a human body) and an insulative garment of a specific thickness."

Richard,

It seems all my questions were answerred, and all my inaccurate assumptions have been corrected.

This thread turned out to be very educational for me, and I thank you for taking the time to chime in and improve my understanding of the matter.

Ivo,

You are quite welcome!