An idea for improving the warmth-to-weight of an Apex quilt – feedback please!

[Geoff Caplan]

Please see below…

[Geoff Caplan]

The experienced folks here have saved me a fair bit of grief by shooting down some of my dafter ideas.

Well, I have another off-the-wall idea, and I’d appreciate your feedback.

I’m thinking of making Apex quilt, and I’m wondering if there’s a way to improve the less than stellar warmth-to-weight ratio of the insulation.

My basic idea is to take advantage of the continuous structure of the Apex sheets by cutting them up and layering them in a way that would create small air-pockets.

One approach would be to build up offset layers of strips in alternate directions, creating air pockets between the layers. This would be using a thin grade of Apex – something like this:

The strips would be wide enough to keep their structure over time and would be held in place by basting stitching. They could be inter-woven or laid flat. It might be necessary to add a thin continuous sheet of Apex to the top and bottom of the pile to reduce convection.

An alternative would be to use two or three continuous layers of thin Apex, but separate them with strips or blocks of thicker Apex in-between the layers.

I’d be grateful for any feedback:

1. Would this idea actually increase the insulation? Or do small, un-insulated air pockets simply cause heat-loss by convection?
2. Would it have any other drawbacks?
3. If there is any value to the idea, what would be the best way to implement it in practice?

Thanks!

[Edward John M]

It might do if the layers were woven as you can do with strips of fur but I actually see no practical advantage.
APEX is what it is, my experience is that the biggest factor is the wind resistance of the outer shell. I was under the illusion that the advantage of APEX was the simplicity of construction coupled with the relative cheapness of the fibre fill

[Jerry Adams]

I think thin layers of just air provide about the same insulation as if the thin layer was filled with insulation like apex or down

For example, on double pane windows there’s an air space of maybe 1/2 inch which provides insulation.

If the layer is thicker than 1/2 inch or 1 inch, then you start getting internal convective currents

You could sew one inch strips of apex to the face fabric, on each side of the strip, then have one inch spaces between strips.

Sounds like a lot of work though, won’t save a lot of weight.  Don’t do it on the shoulders.

Maybe the apex would shift around or something.  All those rows of stitches will compress the insulation and reduce warmth a little.

I did that with a down vest – 2 inch baffles with 1 inch loft, separated by a 2 inch space.  It’s like every other baffle is omitted.  I wear it in the shoulder season, like above freezing.  It seems warm enough but I haven’t measured it or anything.

I’m not recommending for or against.  I don’t think next time I’ll do a down vest like that.  Maybe…

[DAN-Y]

I see no advantage.

[Geoff Caplan]

Hi Dan

Can you expand a bit on your reasoning?

[Geoff Caplan]

Jerry – I like your idea of sewing strips onto a continuous sheet – it would provide more stability.

I would have to hand-sew with basting stitch, though – machine stitching would create cold spots, as you say. A bit tiresome, but for me half the fun of making our own stuff is that we can try things that wouldn’t be economic for a commercial operation.

So the idea is forming for three or four layers of thin sheet, with thicker strips sewn between them in a way that would form small, square air pockets. The sheets would have to have enough structure that the pockets kept at least some of their gap, so I’d probably have to play with different thicknesses.

As you say, probably best to just use standard sheets around the shoulders where there will be stress on the fabric – the air pockets would just collapse.

Relatively easy to test. I could fill a couple of containers with hot water and place them under two squares with the same weight of Apex – one with the air pockets and one without.

[DAN-Y]

Would this idea actually increase the insulation? Or do small, un-insulated air pockets simply cause heat-loss by convection?

 

Un-insulated small pockets of air are not beneficial.

[Jerry Adams]

Then double pane windows on your house aren’t beneficial

Almost all insulation in clothing is from the air.  The down or apex inside just pushes the inside and outside fabric apart and reduces internal convection currents.  Ignoring radiation and evaporation.

A pocket of air as long as it’s only 1/2 or 1 inch thick is almost as effective as if it was filled with insulation

At the shoulders you need some stiff insulation to push out the fabric.  The weight of whatever you’re wearing pulls it down, compressing the insulation.  You don’t want air pockets there, the inside and outside fabric will be pushed together so there’s no insulation.  The bottom 2/3 of the garment is just sitting there, you don’t need much to push apart the inside and outside fabric, although the wind can blow them together.

The reason to do this is it saves weight, but how much?

My vest has about 1 yd2 area.  0.7 oz/yd2 inside and outside fabric.  2.5 oz/yd2 apex.  0.5 ounce for zipper = 4.4 ounces.  That’s about what it weighs on a scale.

If the bottom 2/3 was half air pockets I’d save 0.8 ounces = 3.6 ounces

Hardly worth the effort in my opinion.

In my down vest, you have to sew baffles anyway.  It’s like every other baffle on the bottom 2/3 of the vest has no down in it.  Not really any extra effort so maybe it makes sense.

With apex, you’re supposed to sew around the perimeter to keep it from sliding in, leaving an area on the edge with no insulation.  I’ve done that before – inadequate sewing around the perimeter – the insulation shiftss inwards

If you had strips, theoretically you’d have to sew on each edge?  Maybe it doesn’t make any difference since there’s an air pocket anyways?  With crisscross strips forming a sheet it would be more complicated.

I like out of the box ideas, never know where it might take you.  I would like to know if you learn anything interesting.

 

[Geoff Caplan]

Thanks Jerry

Let’s dig into the figures to see how your idea might work.

A reasonable base assumption is that the quilt is 3 sq meters for a medium sized guy.

Weight of shell

An Argon .67 shell is 23 gsm so the lightest possible shell will be 23 x 3 x 2 = c 140 grams.

Weight of conventional Apex insulation

For a 20F/-6C quilt, we would need 3 sq meters of 267 gsm Apex = c 800 grams.

So the total weight with conventional construction would be 940 grams + fittings.

Potential savings

Let’s say we have 3 layers of 67 gsm Apex, the thinnest on the market.

The layers would weight 67 x 3 x 3 = c 600 grams with little room for weight savings.

So you’d have to use just 2 layers on the outsides, with a single layer of pockets in the middle.

The two layers would total 67 x 3 x 2 = 400 grams, so  now we have 400 grams to play with.

Let’s say the strips are 167g Apex @ 32mm. This would give us a thicker quilt than the conventional construction, but it would be a bit less efficient so let’s assume it would hit the same rating.

And let’s assume that the pockets make up 60% of the area. So the weight of the pocket strips would be 3  x .4 x 167 = 200.

So there is potential saving of 200 grams. Including the shell, this would be around a 20% saving which is fairly significant. It might also breath a bit better and be faster drying.

If you were shooting for a 10F/-12C rating you have more thickness to play with and could achieve an even higher saving.

Of course this assumes the pockets hold their shape and have roughly the same insulating efficiency as the Apex.

I’m thinking of the Apex for a long and potentially very damp project. The question would be whether it would offer much over a down quilt with lots of overfill to help with resistance to damp. Other advantages are a cheaper and easier build. Hmm.

[Edward John M]

Double pane windows use a 12mm gap because that is a compromise between insulation and soundproofing. Air can circulate by convection when the gap becomes greater than 6mm. Yes a gap between sleeping bags when using double bags is “free” insulation but there must be a limit to how effective such holes in insulation would be.
I also see one more issue.
The makers of APEX do state that when using multiple layers of the batting that there should be a layer of scrim between each batting layer, I don’t ssee how that is possible with a woven blanket such as proposed.

[DAN-Y]

I agree with Moondog55

[Jerry Adams]

quick google https://ecoeco.com.au/double-glazing-air-gaps-whats-best-myth-vs-truth/

the insulation value of an air space increases a lot up to 6 mm (1/4 inch)

then increases some more up to 12 mm (1/2 inch)

no increase for bigger air gap

that’s for a vertical window of glass, a horizontal surface of fabric would likely be different.  And air spaces that are narrow strips.

so, my 1 inch was maybe optimistic, just a quick internet comment

I could measure it : )

[Jerry Adams]

and now we’re into something annoying about the internet (and real life)

people arguing about who’s right

[Edward John M]

Makes sense then when compared to air space between clothing layers.
It’s just a personal opinion now, but I still don’t think the benefits if any would justify all the labour involved when the working life on APEX is only about 5 years before significant loss of loft.
Although my old Polaragard garments don’t seem to be that much less warm than when new.
It’s actually quite hard to tell empirically when feeling the cold more is part of the ageing process.

Geoff you do ask some very interesting questions and full marks for moving outside the box

[Jerry Adams]

“but I still don’t think the benefits if any would justify all the labour involved”

yeah, I agree with that

one of the benefits of Apex is you just have to sew around the perimeter

[J-L]

Most double pane windows are filled with a gas, typically Argon – better insulator than just air.

Trapped air is still a reasonably good insulator though. With this design, I don’t see you how would trap enough air to make it worthwhile. Other ways to save weight on Apex quilts could be: using half thickness on parts that would be under your body, using mesh as the liner. Timmermade makes a synthetic jacket with a mesh inner. If you use tulle, you can get weights down to 0.25 or 0.3 oz/yd^2.

[Geoff Caplan]

Yes – if I go with Apex I was thinking of a mesh inner. Apparently the lightest RBTR mesh has a pleasant feel and lasts quite well. And it speeds drying. So a small weight saving there.

The Timmermade false bottom idea would save a little more, allowing you to cut the bag very narrow. Though that’s offset by the need to carry a strap.

Plus you save a tiny bit of weight vs down by not having to use baffles.

[Robert F]

Would be good to optimize the cut of the quilt. Make it small to minimize dead air, but big enough that you don’t have to wrap it around you tight or struggle to avoid drafts. 3 square yards of insulation is probably a very generous cut.

you could also try variable insulation in different parts of the quilt. The sides of the quilt that end up getting tucked under you could be a lighter insulation than the rest of the quilt. There are probably other ways to vary the insulation levels to optimize warmth to weight.

I generally use apex insulation up to about 3.6oz/yard. If warmer insulation than this is called for I use down. If you have a 3 season down quilt, you could make an apex overquilt in the ~14oz range with 2.5oz/yard insulation. This should greatly increase the comfortable temperature range of the down quilt. It also keeps the down dry maximizing its warmth to weight.

[Craig B]

I think one fairly clean way of doing it would be to make a ‘honeycomb’ out of your insulation.  If you put holes in a regular pattern (hexagonal close pack) that are no more than about twice the diameter of the thickness, they will make nice voids in between the inner and outer shells.  You can arbitrarily take out a certain % of the area.  I’d start with removing maybe 30% and do a small scale test like you were proposing.  This arrangement would lose loft a little more quickly than without holes, but maybe not too bad.  They rate wire cloth and filters this way; % open area.  If you want to get really tricky, you could do it with two separate layers of insulation, the when you lay them on top of each other, do it so the holes don’t line up.

It would be pretty tedious to cut all those holes, but that’s the beauty of doing something custom yourself!

[Jerry Adams]

I was thinking about that while hiking

Yeah, make holes in apex

Apex is pretty flimsy stuff.  At risk of falling apart.

Maybe make holes in the apex with a hot punch of some sort that also seals the edges around the hole.  That will give the remaining apex a little more structural integrity.

[Geoff Caplan]

Yes – I think you guys are on the right track here.

I suspect lots of little holes would work better than a smaller number of big holes – otherwise the integrity of the material might be compromised too much. And there’s also the question of recovery from compression which would have to be tested – there may well be a reason why no-one is doing this, given that it’s a fairly obvious idea.

Doing the math, I don’t think I can get close enough to down for a colder-weather system weight wise, but I do think Apex is more competitive for a 2 season quilt so I may play with this idea for that application.

[Jerry Adams]

down has about twice the r value as the same thickness of Apex

If the total area of holes in the Apex that you cut was half of the total area, then it would match down

Maybe if half the area was holes, it wouldn’t hold out the outer fabric properly.  Or something.

2 inch square holes separated by 1 inch spaces would be about right

[Craig B]

It’s a good thought about the hot punch and sealing the edges of the cut Jerry, but that will permanently collapse the loft at the hole.  The apex will not resist being pushed down as you apply the punch, then the whole thickness will just melt together.  Unfortunately, I think you’ll need to cut it with a blade Geoff.  You might try something like this: https://www.mcmaster.com/33785A33/

I’m not sure it will be sharp enough to get a good cut though (I’ve used these to make gaskets), and it’s a bit pricey just to try out.  You could try a rotary cutter, but they are really hard to cut tight circles with, and if you cut squares, it’s hard to control the start and end of the cuts precisely.

The really clean way to do it would be to throw it on a laser cutter, and maybe compress it slightly with some thin cardboard on top.  But that requires a laser cutter….

[Edward John M]

Air woulds circulate in any hole larger than about 6mm and definitely in a 25mm hole so I see no advantage there. Synthetic insulations are already manufactured at the optimum density and I don’t think the factory determined rate can be improved upon.

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