Anyone try this, synthetic insulation combinations?

minor point – the volume of polyester or polypropylene is a small percentage, it's mostly air. (You can weigh a piece of insulation, look up density to find what the total volume of polyester/polypropylene is, calculate total volume of the insulation piece).

since the volume of p/p is small, the total conductivity is determined by the air, conductivity of the p/p is insignificant. If there is a difference between polyester and polypropylene, it doesn't make any difference

you could use steel wool or whatever and it would be the same even though steel is a good conductor

one thing bad about down/synthetic hybrid is, the down has a long lifetime – loft doesn't degrade with time. synthetic has a much shorter lifetime – you lose loft over time. a shame if the synthetic part of your garment has worn out but not the down.

I realize it's primarily the trapped air that is providing the insulation, but i don't fully agree that the material involved doesn't matter at all.

Take a look at that Outerbounds fleece chart i linked on another thread. They supposedly measured the CLO value of similar thickness fleeces, one made out of PP and the other the typical polyester fleece, and the PP was found to be 15% warmer but 20% lighter.

Why the difference, because PP the material itself is less thermally conductive (also with a lower specific gravity so lighter). The fleeces if using similar sized fibers and similar density are trapping the same amount of air though.

If you took loose fill insulation made out of cotton and made out of PP, made of the same fiber diameters and length and with the same volume of fill, you're telling me that they will be equally warm/insulating in effect?

Also i'm not talking about combining down and synthetic on this thread. But since you mentioned it, of course the synthetic is going to lose it's loft before the down. However, good synthetic like Apex still lasts long enough to be practical. The point of combining them, is to get some of the best of both worlds. The lightness and greater thermal insulation of down, combined with synthetics greater warmth when wet for those "oh crap" situations wherein the down looses loft due to direct wetness or sustained high humidity on longer trips. In a combo, at least you have the backup of the Apex and some cutting of the cost of using some synthetic, but for a percentage of the trip you also have the benefits of the down of greater compactness, lighter, etc.

Synthetic-natural blends are somewhat popular and common in the garment and textile world and for good reasons. I don't see why they don't have a place in the insulation world either.

In the low densities of a puffy, Jerry's right, conductivity of the particular polymer is such a minor factor that it can be ignored. In a denser garment like fleece or pile, it would be more of a factor. Conductivity in the insulation fibers themselves takes place lengthwise along the fiber's axis and that's a very long, skinny pipe; a very restricted and convoluted path for the heat to take.

And yet, the material matters. Not for its thermal conductivity, but for other properties – diameter, stiffness, loft-retention, behavior when wet, even surface roughness would effect its ability to trap insulating air around each fiber. One of the balances being sought is that fibers are larger enough diameter to be stiff enough to resist compression, yet smaller fibers block air movement for greater insulation value.

And therein, you are on to something: A combination of some fibers that resist compression with other, very small-diameter fibers that provide great insulation could make for a lower-weight garment/bag. Most commercial insulations are of a single diameter fiber and of a single composition for inexpensive production. Mixing two fibers to get the two traits could do better.

Other ideas: sealed air pockets (like those air bubbles used for packing material) would allow the insulation to be very small-diameter and light. Effective, but at risk of punctures. And subject to volume changes while at altitude or during air transport.

I have no idea how to manufacture this but something with a dendritic structure (tree like) in which large-diameter fibers have medium fibers coming off of them, which in turn in have small fibers bonded to them and then very small fibers are how feathers and down are structured. It is easy to grow dendritic crystals and obviously possible to code their formation in DNA, but I'm not sure how it would be produced with modern polymers.

Good points David, although i have to ask if that is completely true, then why don't companies making insulation fill ever use nylon since it's lighter than polyester, more durable, and just as easy to manipulate the structure? Could it be because there is a significant difference between polyester and nylon thermal conductivity wise? I don't know–could also be because of difference in hydrophobic levels i suppose (but then again, nylon is still basically hydrophobic)?

In any case, i would prefer to use polypropylene fibers anyways since it's the lightest polymer, and the most hydrophobic.

Interesting alternatives and thinking there, but way beyond my current abilities to implement.

> If you took loose fill insulation made out of cotton and made out of PP, made of the
> same fiber diameters and length and with the same volume of fill, you're telling me
> that they will be equally warm/insulating in effect?
Since the insulation comes almost entirely from the boundary layer of air trapped around each fibre, yes to 99% or better.

Cheers

> why don't companies making insulation fill ever use nylon since it's lighter than polyester,

cost
cost
cost

Cheers

maybe polyester is stiffer so it lofts better?

here's the calculation:

polypropylene is 0.885 g/cm3 (from wikipedia). they don't give the density of polyester but it's similar. I think

my 2.5 oz Apex sample is 2.42 oz/yd2 and 0.7 inch loft, so it's 125 oz/yd3

there's 91 cm to a yard and 28.5 g in an ounce, so that's 0.0046 g/cm3

so 0.0046 / 0.885 = 0.005 is the fraction of the apex that's plastic. 0.995 is air.

the thermal conductivity of nylon is 0.25 W/mK. wikipedia doesn't give it for polypropylene or polyester but they're similar. The thermal conductivity of air is 0.0257 w/mK – about one tenth.

ignoring convection and radiation and evaporation, and making a worst case assumption about how the fiber was distributed inside the insulation, the themal conductivity would be 0.995 * 0.0257 + 0.005 * 0.25 = 0.027 W/mK = 4% worse than just air

so, bottom line, the polyester fiber inside the insulation does conduct heat better than air, but because there's so little of it, it only makes the thermal conductivity 4% worse than if it was just air

so, it makes little difference whether the fiber is polyester, nylon, polypropylene, or other plastic, based on the difference of thermal conductivity

"polypropylene is 0.885 g/cm3 (from wikipedia). they don't give the density of polyester but it's similar. I think"

Polyester is about 1.34 to 1.4 depending on what source you consult. I would say that Polypropylene is a significantly lighter material, about 40%.

if you use 1.4 g/cm3, then the plastic is 0.0033 of the volume

the conductivity of the insulation including the plastic is 3% worse than just air using those assumptions

so, it makes little difference whether the fiber is polyester, nylon, polypropylene, or other plastic, based on the difference of thermal conductivity

I understand what you are saying Jerry, i'm just saying that PP is more practical in being lighter weight (and more hydrophobic) if not significantly different thermally–you guys more or less convinced me on that point (though i would be interested in hearing what Richard Nisley would say as well).

The proposed project is a quilt, with one layer of 2.5 oz Apex, and some PP microfiber on the top and bottom. I probably won't use much of the loose stuff though, just looking to boost the Apex some.

Thanks for the feedback

A history lesson: Back in the late 1970's, REI offered a synthetic/down bag. The synthetic fill was in the bottom half where it compressed less and the down was only in the top where it got to full loft and offered its weight and compressibility advantages. I had one. In many ways, I preferred to either 100% down or 100% synthetic.

Then thermarests came out and compressing the insulation below you wasn't such a worry.

I realize you talking about mixing insulations in the same baffles, but it's interesting how ideas repeat themselves.