Seam construction for an Apex mummy bag?

Yeah, managing all those layers is tricky.  So easy for some of them to slip relative to each other as you’re sewing.

What I do is Mark a line with a white “water soluble marking pencil” where I want the edge of the finished product to be.

Then cut all the layers to be over size by at least one inch.

Then put in some hand stitches through all the layers along that marked line.  Corners.  Occasional places in between.

Then sew through all the layers along that line.

Then cut off the outside layer 1 inch wider than the marked line.  Cut off the other layers as close to the line as you can get – 1/8 inch.  Or bigger, it doesn’t matter.  Just don’t accidentally cut anywhere inside the line.

Then fold over the outside layer twice and sew through that to make a clean finished seam.

Just one way to do it.

Nice project, apex bags are pretty rare.  What will the packed volume be?  My EE Apex 20F quilt (0C comfort) is 13L minimum packed size.  Apex R value degrades if compressed too far.

Yeah, I made an apex quilt but I needed a warmer version but apex is so bulky and heavy, so I switched to down

David

We’re going a bit OT here, but I’m curious about the source of your claim that Apex degrades significantly unless babied in the pack?

This is certainly true of a low density chopped staple fibre like Primaloft Gold, loosely held together by heat welding. In my experience it dies far too quickly in real life use – it’s off my shopping list.

But Apex as you know is a continuous filament fibre which is a bit of a different beast. I’ve been assuming it will stand up to any reasonable stuffing short of using a compression sack.

Sources include thru-hiker reviews of the EE Torrid puffy lasting hundreds of days, and the fact that so many militaries around the word specify Apex for sleeping gear.

But my main source is Jerry Wigutow of US bag maker Wiggy’s. He has approaching 40 years of experience with the material and supplies the military and expeditions. He knows it inside-out and he’s very bullish about its resilience. He calls his version Lamilite because he uses a proprietary scrim. but the insulation layer is the same.

He vacuum packs his bags under 20 tons of pressure for storage and shipping. He supplies them that way in USAF emergency kits and says they last indefinitely – here’s what happens when he cuts one open after months of extreme compression:

https://youtu.be/fcPLsWD6Ldg?si=i-Xeexb387Ax3aAy&t=1136

He doesn’t supply a loose storage sack because he believes it’s not needed. He advises customers to simply store bags in the stuff sacks supplied.

Plenty reviews on his site by customers who have been using his bags regularly for 20 years.

It’s not as though down is everlasting either. For example the 900 FP  down in my mummy hood has completely disintegrated under the pressure of my head – no loft left. Needs an expensive re-fill. So it’s swings and roundabouts?

He starts opening up the bag at 19:00.  If he had used scissors it would save a couple minutes : )

Yeah, that bag lofts very quickly even though it was compressed at an extreme level.

Another question is, what if you compress in your pack and then decompress many times, like in normal use.  Would the loft gradually decrease?  I have an apex vest that after years seemed to lose some loft.

Did you try washing your hood to see if that restores it’s loft?

I have read that down will last a long time without losing loft if you don’t let it get dirty, like from body oils.

Jerry – let’s discuss weight. Bulk doesn’t worry me much within reason – pack space only costs grams.

My fancy down bag is reaching end of life and I can’t really afford a like-for-like replacement. I’ve used down all my life but it does have it’s down-sides – pun intended.

My old Fairy Down bag from the 60s was probably south of 600 FP – that was as good as it got back then. It lasted 20 years and was impervious to damp – but weighed as much as a small planet.

Each bag since has been progressively higher FP and has lasted for progressively fewer nights and has been progressively more vulnerable to damp. This last bag was 900 FP and seems to be reaching end of life after less than a decade. I’m a pretty regular user, so my experience is likely different from the occasional weekender, but these very fine clusters do seem quite delicate and need regular pro cleaning at $50 a throw.

An efficient MYOG down bag is a formidable project – and pretty spendy, even sourcing my down from Cumulus. So I started to look at Apex. Performance claims from MLD, Blue Bolt and others surprised me – they weren’t much worse than top of the range down warmth for weight. And it’s a FAR cheaper and less intimidating build. I found plenty of reviews that verified the claims.

So I did some research, and to counter the lower CLO, it’s less impacted by damp and by body oils, the insulation is uniform and doesn’t shift or clump, it’s easy to wash and refresh on the trail, it dries FAR more quickly from overnight damp…

But most interesting to me is the potential to easily make it close fitting. I positively enjoy being cocooned in a narrow bag, while commercial bags have to cater for folks who want more space. So there’s an insane amount of dead space in my current mummy around the hips, where you really don’t need room for movement.

Research by PHD Designs found that dead space is more costly than most realise – it needs to be heated and loses warmth aggressively through local convection.  Field trials have found that a 200g down filler bag that eliminates the dead space gives a 5C to 10C performance boost!

So my idea is to save weight with a tight cut. My down puffy and trousers would fill the dead space and give me 5C+ boost, and the same for a down filler bag or blanket. Rough calculation suggests I can bring this at around 800g for a zero C rating, which I can live with.

Also, there is the potential to body map the insulation very precisely which is tricky with down. I sleep on my RHS and the top of my left hip is where I feel the cold. I can trivially add extra layers of insulation in that area, which should significantly boost the overall performance. My chest never gets cold, so I can save weight there.

I’m hoping that by compounding all these advantages I can enjoy the low cost and convenience with only a modest weight penalty?

Jerry – we overlapped.

I suspect that Apex will degrade a bit more quickly than down, but it’s a fraction of the price and a quick build so there’s that. It should certainly last for a thru-hike though. My main concern is to get the weight into a sensible range – see above.

As for my hood – no, there is catastrophic mechanical damage. Seems that high-end down clusters can’t cope with the weight of a head. I’d have to repair it myself – RAB’s quote was uneconomic.

So any future Apex or down bag is going to be hoodless – because the hood seems to die first. Lots of advantages to a separate hood – you can leave it behind in the summer, use a different type of insulation, substitute for a beanie or balaclava, wash it on trail, wear it around camp etc etc. Very few commercial options as yet, but Nunatak offer a fabulous looking zipless version at a very fair price once Jan gets back to the business.

I had a down bag from ~1970.  It lost loft.  I wonder if I still have it.  This was before I knew about cleaning it.  If I can find it, I could try washing it, but it’s probably 600FP or whatever.

Does down wear out?  Are the clusters delicate and break?  I don’t know, but I vaguely remember reading of people using down for a long time without problem.

I made a down vest.  The collar has lost a lot of loft.  A couple years of use.  I could wash vest and I bet it would fix the problem.  Instead, I made a collar.  Out of apex because it might get wet.  That goes over the collar of the down vest that has lost a lot of loft.

Sort of like you thinking maybe hood on a down bag is a bad thing.

My bag just goes around my neck, then I have a separate hood.  Out of apex because it might get wet.

Also, the collar and hood are such a small area it doesn’t matter if it’s bulky to pack or heavy.

It would be annoying if I again brought up that with asymmetric baffles a down item isn’t as difficult.  About half way between an apex quilt and a regular down quilt.

Did you make the Apex hood? I like the idea but the MLD one would cost a fortune shipped and imported. I’ll have surplus from the bag, so guess I could have a risk free go at a MYOG version.

The Timmermade guy has some interesting ideas – but maybe over the top for the conditions I camp in…

https://timmermade.com/product-category/balaclavas/

Hi Geoff, Stephen measured loss of Apex R-values vs number of compression cycles here

Also, when I asked EE, they recommended to not compress their quilt beyond a certain point (13L) or it would accelerate loss of  r-value.  OTOH Stephens results showed similar r-value degrades with 20 vs 70lb loads, so either EE was just guessing or Stephen’s weights didn’t simulate extreme compression enough.

Good call on hoodless.  Much more flexible, beanies to balaclavas

For a tight fitting apex bag, I’d go 7D, 10D heaviest.  On cold nights I wrap my 10D apex quilt tight right around me and wouldn’t want a shell any less breathable.  I also have a pretty light (by synth standards) tight fitting 0C comfort synth bag and it gets brutally clammy due to the 40D shell.

Of course I made my own apex hood :)

Good project with scraps.

You could make a collar too. Maybe gloves or mittens.

David

I did read Stephen’s test. But as he admitted himself, 30 cycles isn’t exactly definitive.

He’s assuming that degradation will continue arithmetically – but perhaps all he’s measuring is an initial settling in? Without a longer test we don’t really know.

I do find it very hard to believe his preliminary result Primaloft Gold performs better  – in my own experience it collapsed unacceptably fast. That’s not what I’m seeing with reviews of Apex products.

In the end, all gear deteriorates on the trail. It’s a relatively inexpensive project – so long as I get a few years out of I’d be happy enough…

Getting back to the original question.  Back when synthetic insulation had to be quilted, Some layers of insulation were sewn to the lining and some to the outer shell of the sleeping bag.  The quilting lines could be offset.  If you did that with Apex, you could have fewer layers to sew through at once.  If the lining and shell units are connected at the zipper, head, and foot, the long side seam would not be one sewn-thru cold spot. ( A bag within a bag).  I’m working on an Apex quilt and thinking about how to eliminate the cold seam at the foot end.

Does anyone do a differential cut with synthetic insulation? The insulation does not fall away from high points like hips, so probably not needed. But you could save a little fabric in the lining.

The other thing I remember from sewing a synthetic quilt in the past, was being surprised by the finished product being slightly smaller than the cut fabric dimensions.  It lost a couple of inches in length, etc..

Scott

with apex, you only have to sew around the perimeter.  Don’t need in between quilting.

maybe the finished product is shorter because a little of the length is used up to provide the loft length.

like, with a 3 inch air mattress that’s 20 inches wide uninflated, when you inflate it it becomes 17 inches wide, or maybe 18 inches because it curves over the edge.

if you tuck the edge of the quilt under you it won’t matter that it’s sewn through which provides zero loft.  That part is under, so it doesn’t matter.

I have sewn clothing with two layers of Polarguard 3D, which had handling characteristics pretty much the same as Climashield, and a quilt with a single layer of climashield, and a detached hood with two layers of climashield.

My approach is to minimize seams that include all the layers. For a sleeping bag, you only need to have all layers meet at the top edge and at the zipper (if you have a zipper). Everywhere else, you have a layer of insulation sewn to a layer of fabric and you join two of those. No need to attach inner to outer at the foot of the bag or up the side. Also, to avoid bulky seams, you can offset the seams in the inner from the seams in the outer.

One thing I found is that it is all too easy to stretch the insulation while laying it out for cutting, and then it relaxes after and ends up smaller than the fabric. So be sure the insulation is not stretched, and cut it a little bigger than the fabric just to be safe. If you then align the edges when sewing insulation to fabric, your worst case is the insulation is larger than the fabric, which will not cause any problems.

Differential cut is a must if you have significant loft, especially if you are aiming for a colse fit. Do the math as if you had two cylinders, and two inches of loft means the outer shell should be 12 (yes that’s not a typo, 12) inches larger circumference than the inner in order for the insulation to loft fully. Of course you can get away with less when there is more room inside the bag, since the insulation can push into the empty space. But you said you want a close fit.

Like Jeff sez, stay away from Primaloft. My experience with “Prima’loft’ loft retention is horrible.

I know Wiggy’s fills are very resilient and that’s why the Brit military likes it. The US military has found Climashield is very resilient  and uses it. As Jerry sez, Alpha Direct is bulky, even the light Alpha 60 I’m using as a mummy bag “frost catcher”.

Primaloft has gone through a number of interactions each supporting a different subcategory. Apex had the advantage of no baffling and in my opinion can be warmer than a layer of thin down at the same weight. I find over time that Apex stretches and develops thin spots. I prefer Primaloft at least some forms of it. I don’t have the knowledge to be more specific.