Down fill power vs amount comparison chart, does one exist?

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Down fill power vs amount comparison chart, does one exist?

Postby JCB81 » Tue 01 Aug, 2017 1:06 pm

I don't know if anyone has ever done any research on this, or some kind of chart exists, but i'm trying to figure out a way of comparing the amount of fill vs the fill power quality for the equivalent warmth?

So for example product A is filled with X number of grams of 500 fill power and product B is filled with X number of grams of 800 fill power. So how many more grams of down would product A need to be the same warmth as product B?

I appreciate its probably not that simple as the material that holds the down that is going to make a difference if they are different between products, the % of down/feathers may be slightly different, and the way its stitched, but you might be able to get an indication to make an informed comparison?
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Re: Down fill power vs amount comparison chart, does one exi

Postby wayno » Tue 01 Aug, 2017 3:26 pm

most outdoor down gear has a high percentage of down in it, 90% or above, it comes down to the quality of the down.. down from older animals lofts better, theres less of it available and its more expensive to buy... how much it lofts is the biggest determiner of warmth, ALTHOUGH, in high winds, high lofting down compacts more when you're wearing a down jacket or sleeping out in the open. montbell rate the lowest comfort temperature of the clothes they make, not sure of other brands that may do so.
its complicated by the construction of the goods, how the compartments of down are made , stitch through versus baffles and the type of baffles if they are slanted to avoid cold spots, and how deep thee baffles are,
stitch through down gear is colder, the more stitch through seams the more heat is lost... all but the best down clothing is stitch through. most sleeping bags have baffles of various designs... pays to go for a brand that is known for making warm gear, they will construct the gear so minimal wars is lost. anyone can make down gear that loose too much heat, not every company makes gear that minimises heat lost efectively....
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Re: Down fill power vs amount comparison chart, does one exi

Postby crollsurf » Tue 01 Aug, 2017 3:44 pm

I asked a similar question not long ago http://bushwalk.com/forum/viewtopic.php?f=15&t=25730
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Re: Down fill power vs amount comparison chart, does one exi

Postby Orion » Tue 01 Aug, 2017 7:29 pm

JCB81 wrote:So for example product A is filled with X number of grams of 500 fill power and product B is filled with X number of grams of 800 fill power. So how many more grams of down would product A need to be the same warmth as product B?


Warmth is proportional to insulation thickness. So if the down is dry and new you can simply compare insulation volumes.
In other words, equal warmth will be achieved when A_grams * 500 = B_grams * 800.

That's for brand new down that's dry. It's not so easy a question to answer for down that is not new anymore or down that contains significant moisture.
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Re: Down fill power vs amount comparison chart, does one exi

Postby wayno » Wed 02 Aug, 2017 4:10 am

some down is chemically treated to resist moisture and will retain more loft when damp and dry out a lot faster..
it will be in the details about the item if it has this sort of down. and it won't be cheap
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Re: Down fill power vs amount comparison chart, does one exi

Postby Orion » Wed 02 Aug, 2017 7:27 am

wayno wrote:some down is chemically treated to resist moisture and will retain more loft when damp and dry out a lot faster..
it will be in the details about the item if it has this sort of down. and it won't be cheap


Premium down is expensive whether treated or not.

900 fill white goose down - $13.33 USD per ounce
850 fill HyperDRY goose down - $12.67 USD per ounce
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Re: Down fill power vs amount comparison chart, does one exi

Postby simonm » Wed 02 Aug, 2017 7:39 am

Orion wrote:
wayno wrote:some down is chemically treated to resist moisture and will retain more loft when damp and dry out a lot faster..
it will be in the details about the item if it has this sort of down. and it won't be cheap


Premium down is expensive whether treated or not.

900 fill white goose down - $13.33 USD per ounce
850 fill HyperDRY goose down - $12.67 USD per ounce


The HyperDry treatment actually adds very little to the cost at the wholesale end but I guess it's good for profits for retailers to suggest otherwise.
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Re: Down fill power vs amount comparison chart, does one exi

Postby Mark F » Thu 03 Aug, 2017 7:21 pm

To get an equivalence from say 900 loft down to 600 loft you will need 50% more 600 loft down to fill the same volume than 900 loft down. You need first to work out the volume of the space to be filled,then divide by the loft of the down to get the initial weight. It is normal to over fill by at least 10% or often quite a bit more.
The loft value is a measure of volume where the down is placed in a cylinder with a light weight on top.The volume of the cylinder is measured where the light weight settles.
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Re: Down fill power vs amount comparison chart, does one exi

Postby andrewa » Thu 03 Aug, 2017 11:46 pm

As per Mark F, but be aware of proportion of quil to feather in down. A down with more quil will weigh marginally more than one without, and also be bulkier - so 95/5 900 loft is pretty well ants pants. Back in the 80s when I worked at Mountain Designs, 90/10 , 500 loft was basic down, 95/5, 550 loft was upper range, and 95/5 700 loft was the ants pants, so we've come a long way.

In fact, I've just lent a sleeping bag I made I the 80's to a mate - at the time it had all the bells and whistles - 1.5oz nylon, extraordinarily complex baffle construction, 1.1 oz goretex outer, and 1kg of 95/10 550 loft down. Total weight was just over 2 kg, so the shell was 1kg, and it kept me comfy down to -12.

It's been replaced by many new bags, but current bag is a quilt with 0.9oz nylon, and 450-500g of 800 loft down. The total weight is about 700g, so the shell is 200g. Still sleep comfortably down well into the negatives, albeit wearing down jacket and pants. More compact, much less weight. All good things.

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Re: Down fill power vs amount comparison chart, does one exi

Postby Orion » Sat 05 Aug, 2017 1:43 am

andrewa wrote:As per Mark F, but be aware of proportion of quil to feather in down. A down with more quil will weigh marginally more than one without, and also be bulkier


I'm not sure I understand. Isn't the weight of the feathers included in the fill power value?

The down I've purchased a few times didn't even specify a down/feather ratio, just a fill power rating and a certification that it met some international standard.
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Re: Down fill power vs amount comparison chart, does one exi

Postby wayno » Sun 06 Aug, 2017 5:12 am

dont worry about the feathers, down in outdoor gear doesnt have much feather in it, go by the loft, the higher loft are likely to have even less feather.
loft is a measure of bulk for a specific weight of down...

https://sectionhiker.com/fill-power-rat ... oose-down/
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Re: Down fill power vs amount comparison chart, does one exi

Postby Orion » Sun 06 Aug, 2017 10:29 am

I know about the method used to measure fill power.
That's why I was asking Andrew what he meant about the effect of the feathers on the weight.

In any case I'm not sure feathers are ignorable. I've read anecdotal reports that lower fill power down, which likely has more feathers, is less sensitive to moisture. The question becomes how a certain loft of 900 fill down compares to equivalent loft of, say, 650 fill down when they are exposed to a certain amount of moisture. The answer to that question is very much a part of what the OP was asking about.
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Re: Down fill power vs amount comparison chart, does one exi

Postby wayno » Sun 06 Aug, 2017 10:42 am

the vast majority of the fill is still down, even in 600 loft down, it can still be significantly affected by moisture if it isnt treated against moisture..
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Re: Down fill power vs amount comparison chart, does one exi

Postby simonm » Sun 06 Aug, 2017 11:10 am

I haven't seen testing done on various fill powers response to moisture but anecdotally lower fill powers are less susceptible to loft collapse when exposed to moisture.

Edit: This is a quote from BPL;

I spoke at length with IDFL yesterday about down testing.

None of their tests stimulate real world testing. 900 fp in a test is going to be a pipe dream in the field, because they steam wash and dry the down to nearly zero humidity before doing the test. Ironically, this most recent iteration of test methods was designed to determine the maximum possible fill power for down rather than what it will look like in the field.

Interestingly as a side note, we did some 900 fp testing of down a few years ago on two manufacturer's 900 bags. We cut the bags open and sent them to IDFL. Neither made the claimed 900 spec (they tested 830-870 using the steam method). What was more dramatic was that when each down (which clearly came from different sources as evidenced by visual inspection) was subjected to 50% humidity, the differences were pretty dramatic. One bag tested at 770 fp, the other at 680 fp. It seems that at least these two sources of 900 down had feathers in it that were not resilient in response to humidity.

The kicker is that we ran the same test next to down taken from a manufacturer's 750 fp bag. at 50% humidity, the fp was 720. Why? It had more feathers that were stiff enough to preserve the loft in moist conditions.
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Re: Down fill power vs amount comparison chart, does one exi

Postby undercling-mike » Mon 07 Aug, 2017 12:17 pm

simonm wrote:I haven't seen testing done on various fill powers response to moisture but anecdotally lower fill powers are less susceptible to loft collapse when exposed to moisture.

Edit: This is a quote from BPL;

I spoke at length with IDFL yesterday about down testing.

None of their tests stimulate real world testing. 900 fp in a test is going to be a pipe dream in the field, because they steam wash and dry the down to nearly zero humidity before doing the test. Ironically, this most recent iteration of test methods was designed to determine the maximum possible fill power for down rather than what it will look like in the field.

Interestingly as a side note, we did some 900 fp testing of down a few years ago on two manufacturer's 900 bags. We cut the bags open and sent them to IDFL. Neither made the claimed 900 spec (they tested 830-870 using the steam method). What was more dramatic was that when each down (which clearly came from different sources as evidenced by visual inspection) was subjected to 50% humidity, the differences were pretty dramatic. One bag tested at 770 fp, the other at 680 fp. It seems that at least these two sources of 900 down had feathers in it that were not resilient in response to humidity.

The kicker is that we ran the same test next to down taken from a manufacturer's 750 fp bag. at 50% humidity, the fp was 720. Why? It had more feathers that were stiff enough to preserve the loft in moist conditions.



It'd definitely be great to see some more testing of down in closer to real world conditions, I suppose there isn't much appetite for it in the major down producers or manufacturers because in the end it's easier to have just one number for marketing purposes and competition has lead to that being the highest number possible as in the current IDFL test.

That quote from BPL has certainly propagated through various internet forums over the years and it provides one data point but I have to say it doesn't really jive with my (admittedly anecdotal) experience. The humidity here is regularly above 50%, sometimes much above and if the performance of, for example, the 950 fill power down I've used degraded disproportionally just with ambient humidity in that range I would easily be able to tell when filling my quilts. If anything the loft of the 950 fill seems maybe slightly more robust. Suffice to say I think there's a lot more to the story but in my experience so far with a fair variety of down types from a range of sources the fill power number seems to be a reasonable measure of the relative performance.

On the comment about feathers preventing loft collapse I'd say this is just conjecture, in all of the high fill power downs I've handled (750fp+) the feather content is a fairly small proportion of the weight and a tiny proportion of the loft. This was also true for an older 650 fill bag I cut open to harvest the down at one point, although that down had more feathers the amount of loft provided by those feathers was small compared to the loft of the down clusters, and certainly not enough to maintain performance if the clusters collapsed. So just looking at a variety of down sources it doesn't look like the feathers present make a significant contribution to the loft, nor does it look like the feathers provide structure that prevents the down clusters from collapsing.

That said, I'm sure there is some difference between different downs in terms of how they handle moisture but I don't think it will necessarily be as simple as to correlate the fill power inversely with resistance to moisture.
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Re: Down fill power vs amount comparison chart, does one exi

Postby Moondog55 » Mon 07 Aug, 2017 12:26 pm

Another way to look at it
Fill weight Vs absorbed water weight
If all down absorbs the same percentage of water won't the higher FP down simply absorb a lower mass of water because there is less of it?
A wet bag is a wet bag and to be avoided but if it happened would you be better off in a bag using the higher lofting down?
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Re: Down fill power vs amount comparison chart, does one exi

Postby undercling-mike » Mon 07 Aug, 2017 12:56 pm

Moondog55 wrote:Another way to look at it
Fill weight Vs absorbed water weight
If all down absorbs the same percentage of water won't the higher FP down simply absorb a lower mass of water because there is less of it?
A wet bag is a wet bag and to be avoided but if it happened would you be better off in a bag using the higher lofting down?



I'm not sure if it's as simple as that, higher FP down generally has more fine structure and more surface area for adsorption (if that's what happens rather than absorption). Of course hydrophobic treatments make a big difference in how much water down will absorb if wetted but even for untreated down the processing could have an effect, such as how much natural oil remains etc.
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Re: Down fill power vs amount comparison chart, does one exi

Postby simonm » Mon 07 Aug, 2017 1:15 pm

It definitely needs some testing to be done to more conclusively say one way or another, until then it's all just conjecture.

The Prolite guys make mention of it in this video -
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Re: Down fill power vs amount comparison chart, does one exi

Postby undercling-mike » Mon 07 Aug, 2017 3:00 pm

I guess there are two separate issues with down and moisture, firstly what happens with the down in response to humidity and second what happens if it gets wetted with liquid water. The humidity issue is the one we don't have a lot of data on (for the liquid water issue we know that hydrophobic treated downs are harder to wet and absorb less water and feathers dry out faster, although my conjecture is that the feathers supply a small fraction of the overall loft in any down you'll find in lightweight equipment).

A lab equipped to do down testing should be able to gear up and design a protocol to do humidity testing (even though the conditioning procedure to get consistent and repeatable results would still mean that it's not exactly real world), so it's kinda surprising we haven't seen any results. No doubt it'd be a lot of work to do a comprehensive job. It'd definitely be interesting to see the kind of variations there are and what factors are important, you might have to test a lot of samples from different sources to get a clear picture. As I said I can easily tell that the 950 fill down I've used lofts more for a given weight than the 800 or 850 fills at ambient humidity (usually well more than 50% but a very low 30% today) and without pre-conditioning whereas the BPL data point says that the 900 fill samples they tested were not much better or even worse than 750 fill down at 50% humidity.

It'd definitely be interested in the results, not sure I'd want to fund the research though...
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Re: Down fill power vs amount comparison chart, does one exi

Postby simonm » Mon 07 Aug, 2017 7:12 pm

I would think the tests have been done by someone but perhaps just not available to the public. Some of the bigger companies would've surely???? We have been doing some testing on the water resistant down v untreated but its fairly basic stuff.
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Re: Down fill power vs amount comparison chart, does one exi

Postby Orion » Tue 08 Aug, 2017 1:31 am

I've seen that quote on BPL and watched that video before too. I consider both "anecdotal" because there's not enough there to go to the bank with.

As an aside, does it really make sense to talk about water absorption and down loft loss with respect to relative humidity without also saying what the temperature is? Where I live the RH is most often in the 60-80% range but it's relatively cool. So absolute humidity isn't all that high. I measured my down quilt straight out of the hot clothes dryer and then 24 hours later and it had picked up about 5% weight, which of course also includes absorption by the shell and baffles. What that extra moisture did to the loft isn't so easy to measure and I haven't tried.

For me the extra cost of premium down is money worth spending. That is, unless you could convince me that higher fill down is denser in actual use.
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Re: Down fill power vs amount comparison chart, does one exi

Postby rjtedge » Wed 09 Aug, 2017 11:18 am

Noting all of the above comments around moisture, fabric choices etc - the maths for comparing down taking both fill weight and fill power is fairly straight forward. I know this after struggling for a with this process a few weeks ago trying to compare down filled jackets.

I ended up making a spreadsheet and finally a little web based script to do the maths for me -https://rjtedge.github.io/downloftcalc/
You just enter the fill weight (in grams) and fill power and the script will tell you the total loft of the product and then tell you how many grams of down would be required to create the same total toft for different fill powers.

For example, a sleeping bag with 500g of 750 fill power down should be as warm as a bag with 417g of 900 fill power down.
Image

Let me know if you want details of the maths etc or if the site doesn’t work for some reason.

Cheers
Rob
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Re: Down fill power vs amount comparison chart, does one exi

Postby Moondog55 » Wed 09 Aug, 2017 11:28 am

What assumptions have you made re sizing when writing this program>
There being a huge difference between an XXS for the tadpole and an XXXL to fit me
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Re: Down fill power vs amount comparison chart, does one exi

Postby rjtedge » Wed 09 Aug, 2017 11:34 am

Moondog55 wrote:What assumptions have you made re sizing when writing this program>
There being a huge difference between an XXS for the tadpole and an XXXL to fit me


This does not take into account shape or sizing of different products. It only considers the loft fill power and weight - e.g. same sleeping bag with different down inside (noting that even this would not necessarily all end up being perfectly equal as you could put in a super high power down and have it collapse under the weight of the fabric of the bag that was designed for 600 fill power down).
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