A REVISED PARADIGM FOR ESTIMATING GARMENT COMFORT LIMITS

[Richard Nisley]

In a week’s time, I received two enquiries from friends plus saw a post on the BPL forum from a Reddit poster all asking about specific garment’s comfort limits. That was the genesis for this document. It attempts to rely on a few of my custom tables and charts, combined with minimal words, to address this topic.

One well known quote of Albert Einstein’s is: “If you can’t explain something simply, you don’t know enough about it.” That was part of the problem when I first discussed this topic in a 2007 forum thread Here. After 11 years, I now know little more about the subject. This revised document covers new insulations, new garment types, and detailed instructions so you can estimate garment comfort limits yourself.

[Richard Nisley]

This is the essence of all you need to know but the details are Here

[Paul S]

Richard, how can I view this without creating a one-drive account?

 

Thx,

P.

[Richard Nisley]

Paul,

Here explains that you do not need to sign in to view this document. Editiing is not enabled for it but, if it was, only then would you need to sign in.

 

[Paul S]

I usually use Chrome, but could not view the doc no matter what I did.(didn’t want to set up yet another account)

So I tried “Edge” instead, it worked!

So, if anyone else is having trouble seeing this great info (Thanks Richard) using Chrome, try Edge, it might work for you!

 

[MJ H]

That looks great, but I have a question about your models. Is there an error term, something that would let you get at intra- and inter- person variation for things that aren’t related to weather and clothing?

[Edward John M]

Again many thanx for all the hard work you do to keep us informed. Interesting to me it that a lot of the new LW and UL fabrics available locally are far too tightly woven to make optimum airflow windshirts from but old fashioned poly-cotton sheeting seems almost perfect at only a slight weight penalty

[Richard Nisley]

MJH,

No there are no error terms in this model. If you need that, then I suggest you use the ISO 11079:2007 model as an alternative.

My objective was try and explain a relatively simple model that would allow an UL backpacker to thwart the problem that the poet Robert Frost best described:

“The sun was warm but the wind was chill. You know how it is with an April day. When the sun is out and the wind is still, You’re one month on in the middle of May. But if you so much as dare to speak, a cloud come over the sunlit arch, And wind comes off a frozen peak, And you’re two months back in the middle of March.”

Robert Frost

 

[Richard Nisley]

Edward John M,

I think the holy grail for windshirt fabrics requires more than just the relatively high air permeability from fabrics like you referenced. It also requires high tenacity for strength combined with light weight, permanent DWR, and an extremely uniform weave for greater > 300 mm HH.

[Edward John M]

Yes Richard and I am still looking, although Nikwax can help Re water resistance. Taslan works but is heavy, an old fashioned wool  shirt in dress weight is perfect but not even close to LW

[Martin D]

Nice work! You might want to factor in the fact thermal conductivity is not a constant for a given material across a temperature range. Every material is different, but there could be a 20% variation across your displayed range.

[MJ H]

My objective was try and explain a relatively simple model that would allow an UL backpacker to thwart the problem that the poet Robert Frost best described:

And you succeeded at that. Thanks.

I just might have an atypical level of interest in regression models.

[Paul S.]

Thanks for sharing, great read.

Can you clarify the Active Insulation comparison table?  It reads like you’re implying that the air gap of a wind shell like the Squamish provides the same insulation as a Nano Air, which is counter to my experience.  You noted in the past that a Nano Air = Wind Shell + 100 weight fleece, which matches my experience (I think the fleece is now warmer after the degradation of the synth insulation).

[Brett Peugh]

So back to a decent fleece and a shell then?

[Richard Nisley]

Martin,

Thank you for your suggestion; I incorported it as an additional document section near the end. Part of that section includes Figure 8 which provides air’s Iclo regression plot for the full temperature range.

[Stumphges]

Richard, thank you so much. Your original graph from 2007 has guided my choices for trips over the past decade.

Does anyone know about the wicking properties of Polartec Alpha, particularly the standalone versions that are similar to fleece garments (Rab makes one)? I notice that Alpha tends to have a smooth inner face with a furry or spikey outer surface. If the properties of the fabric are similar to Polartec’s wicking fleeces – Powerdry and Powerstretch – one would think Alpha would tend to wick inward, toward the wearer, given that those fabrics employ denier gradient knitting with moisture traveling from toward the denser part of the knit (from spikes to tightly knit). Does Alpha wick, and in which direction?

Looking at Richard’s document, it would be nice to have a wicking layer to replace Powerdry or Powerstretch with nearly twice the clo. (Maybe, given these layers are pretty thin and light anyway, it doesn’t matter much, but this is BPL.)

[Edward John M]

If ALPHA does have two faces then I think it is the shiny side out/furry side in. My sample of 60GSM ALPHA was the same both sides. I sometimes use fleecy polyester mesh as a garment lining and that is definitely shiny side out

[Richard Nisley]

Paul,

On the upper range of this active insulation temperature spectrum from 57F to  26F, an optimally fitted windshirt and a wicking based layer will work as well a Nano Air Light Hoody for most people (not all). This assumes that a large air gap under the hoody is sealed well at the neck, wrists, and waist. I end up customizing the majority of my windshirts to accomplish an optimal fit.Those that don’t have an optimal fit, will need the addition of a Polartec 100 insulation layer under their windshirt to match the active insulation layer’s warmth.

[Paul S.]

Thanks for the response.  Is that assuming little to no wind?  I.E. the wind would press the fabric right against your and remove that warming air barrier.

[Richard Nisley]

Paul,

Please look at page 20 of my pdf link in the second post of this thread. It explains this “no” answer to your latest question.

Page 19 of my pdf link explains how much insulation you will achieve from the 6 mm gap in windy conditions.

[Hugh Webb]

Thanks Richard. Great summary.

I really like your worked example of your calculation on page 4.  I follow how you calculate the fabric’s Iclo by subtracting .6 from the clo value (.99) to yield a figure of .39.  But then I’m confused why you calculate the garment clo for a hoody(i.e. .52 bsa) by multiplying .99 x .52?  Surely it should be .39 x .52?  Otherwise why did we go to the trouble of determining the iclo?

Am I missing something?

[Richard Nisley]

Hugh,

I just opened up the pdf document in this forum’s second post link and circled the text I think you are referencing. I suspect you are seeing an older version with typos that is still in your browser’s cache. Please let me know if this is the case?

[Hugh Webb]

Ah yes, thanks. That explains it.  I downloaded the original file when you first posted and only just got around to reading it properly today.  But I’ve now replaced my old version with the up to date version.

[Hugh Webb]

One more question relates to your point that 1 clo is the warmth of the “base ensemble iclo” and equates to the amount of clothing required for a sitting person to be thermoneutral in a 70F room with normal ventilation.  I am trying to reconcile this with your figures on the iclo value of, for example, a cap 4 hoody which is .14 (according to Figure 7)  .  I would have thought a full set of cap 4 thermals (ie including pants) would be more than warm enough to keep me thermoneutral at 70F – but it would obviously be less than 1 iclo .

why do these two ways of deriving the iclo of the “base ensemble” generate such different results?

i also note that the base ensemble includes shoes (and possibly gaiters?) which would presumably affect assumptions about how to factor in the boundary air layer iclo.

[Ken Larson]

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