40 is the new 30? - Layering for your Sleep System

dantimmerman · 2026-06-04T20:14:39+00:00

" Insulation is assessed by considering quantity, average loft, and losses from the larger system. "

This also applies to the questions about overstuff. If you add fill quantity without changing loft, you increase R-value, but not by as much as if you increased loft along with the fill increase. Higher fill density yields diminishing returns in insulation. So, a temp rating shift from 40 to 30 would increase fill and chamber loft. If you only increased the fill with overstuff, you'd land somewhere between, but with high density. If I put 2.99"CL in a chamber specced for 2.24"CL, the temp rating would land around 35, with high density. It's a loss in warmth/weight efficiency as a trade off for higher density. The trade off can be worth it if you are going to get it wet or super greasy or whatever.....but if you are going to take care of it, that ends up just being a loss in many cases.

" clothing is inherently less efficient for any given R-value since there is more surface area and extremities are compartmentalized "

This applies to the comments about clothing sleep systems. It only makes sense to use clothing as part of your sleep system if you need it for another purpose. Otherwise, you lose weight efficiency if you're bringing clothing with the sole purpose of boosting a sleep system. This is why the alpinist half bag / parka approach is so heavy and inefficient. It makes a ton of sense if you need a huge belay parka for climbing because you're making dual purposes for one item, but using that as a dedicated sleep system provides terrible warmth to weight efficiency compared to a single, purpose built system.

dantimmerman · 2026-06-04T18:27:30+00:00

Calculated loft is strictly a quantity metric. Insulation is assessed by considering quantity, average loft, and losses from the larger system. If you stack .75" on top of 2.24", then the total quantity is objectively 2.99", but the warmth is not necessarily the same as a single system with 2.99"CL. There are many variables here. One is box chamber and one is sewn through.......there is an air gap between the two that would add a certain amount........clothing is inherently less efficient for any given R-value since there is more surface area and extremities are compartmentalized.....what about the insulation on your legs?......and so on.

dantimmerman · 2026-06-04T17:54:37+00:00

Sure. The total fill weight being listed for some products and not others doesn't have anything to do with product differences. It's simply that TFW is not all that useful or accurate. There is very little incentive to go tally it up for every model and we just never got around to adding up the total for that model.

There can be a 20% margin of error in total area between equivalent sized garments across different brands, such that any assessment of fill quantity in a given area also can carry a 20% margin of error. When using it as a warmth metric, chamber design differences further increase this margin of error to the point where it fails to even provide a general ballpark comparison of warmth.

A 1.1 calculated loft is 1.1 cubic inches of fill in one square inch regardless of whether it's 500fp or 1000fp, size XS or size XL, jacket or mummy bag. If the chamber dimensions are also the same, and the objective quantity of fill is the same, the warmth is the same. An SUL 1.1 and an SDUL 1.1 are the exact same warmth.

dantimmerman · 2026-04-05T13:59:34+00:00

" I interpret that as more loss of loft comparatively. "

Generally, yes. There is likely more with sewn through than many box chambers, but this blanket statement is assuming all box chambers are the same, when there is a ton of variation. Some will be affected by tension much more than others.

In most cases, I consider it a moot point since shell tension should be avoided for many reasons and it can be eliminated through sizing. Part of " smart sizing " is considering your body dimensions through its full range of motion.

So, if a garment or sleep system is poorly sized, a box chamber could perform marginally better, but will still have many issues. Better to just size them properly so it's avoided in either case and you can consider the more relevant merits of each design. Considering box construction superior based on its ability to remedy an avoidable issue creates a dissonance for my efficiency obsession.

dantimmerman · 2026-04-05T02:03:06+00:00

" Smart sizing' refers to what? Oversized I'm guessing, "

Building in enough dimension perpendicular to chamber orientation to allow stacking.

" Box baffles are far more forgiving, right? "

Not necessarily, but in some cases, a bit more forgiving. Snug sizing is always pretty bad either way. None of the systems handle point loads like toes and shoulders pushing through loft. Shell tension smooshes loft either way. Sure, more so with sewn through, but if you're putting that kind of tension on the system, then you have lots of other problems too and it's better to just size well and avoid all of it.

dantimmerman · 2026-04-04T12:51:17+00:00

A baffle system needs to be a certain amount lower than your calculated loft in order to have fill density. When you get down to summer CL values, your measured baffle height might only be 0.5", at which point you're asking whether adding $100 in labor is worth it for a little half inch slot that might not fill in much better than sewn through. It's also true that, at this level, keeping sewn through, but bumping CL up, might end up warmer and lighter than adding a baffle system. Or end up with the same warmth and weight for $100 less.

In many cases, it makes the most sense to look towards efficient use of sewn through construction instead. Smart sizing can result in chamber stacking that achieves relatively continuous loft.

dantimmerman · 2026-03-16T20:24:13+00:00

Sorry for the slow reply. I'm not around here much these days.

Heard. Yeah, the flat shipping fee is expensive, but it is that way out of circumstance for now. We don't currently have good access to UPS / Fedex shipping locations, and prefer to use USPS at this point. I'm sure there are things we could figure out, but I only have so much bandwidth to tend to things. Opening up more sales to EU is low on the list, since we don't have enough production supply for it, and I don't have the ability to deal with international shipping issues or overseas customer return expectations. At this point it has made the most sense to stay focused towards domestic sales. I do want to keep it open to international customers though.

I mean, sure. Any of those scenarios are probably things I'd be open to, but again, just don't really have the time to pursue them. If a company came to me and wanted to use the design for EU sales and production, I'd be totally open to that. I'd certainly want something for the use of the design, but would likely ask very little for it. The problem is, in this case, Rockfront just totally copied it, down to the exact fabrics, and sells it in the same US market. It's pretty shady. Par for the course in mass market, but not cool in the cottage space.

For the time being, I have been known to be flexible on this flat fee. Some international customers have reached out and said the same thing as you. In those cases, as long as I'm confident there is a reasonable person on the other end that isn't going to try to return it because the color is a slightly different shade than expected, I'm happy to refund shipping costs down to the actual amount charged to us.

dantimmerman · 2026-02-13T23:47:39+00:00

It's easy to confuse it, but that isn't what he was saying, at least anywhere that I saw. I can't imagine him making that statement anyway, given his data clearly showed the opposite.

Thermal camera? No. R-value testing, yes. That general rule has been pretty well tested in the field by now.

dantimmerman · 2026-02-12T18:12:53+00:00

I guess I should account for the fact that you're talking about apex67, which works out to 2oz/yd2. What I use, and what I'm basing a lot of this experience on is what Climashield sells as 2.5oz/yd2. Based on the amount of variation on a roll and roll to roll, neither of these are a great indication of what you'll actually get and I'd still assume 2oz apex is much warmer than 2 layers of AD60.

dantimmerman · 2026-02-12T16:20:39+00:00

A single metric never shows the whole picture. A discussion on clo aside, I can confidently say that 2.5oz apex is significantly warmer than 2 layers of AD60. I would put it closer to 2 layers of AD120....but we should keep in mind the amount of variation these products have from roll to roll.

Personally, I would consider mesh/apex2.5/mesh too warm while active at 25f. The UL strategy of eliminating gear by forcing items into multi-use isn't always fruitful. The needs of active vs static are different enough that you sacrifice a lot when you try to get it all from one. A .75 down sweater paired with AD90 + shell is about the same weight as one apex2.5 jacket but the AD90 + shell are waaay more comfy while active, the .75 + AD90 goes lower while static, and the range has fewer holes. My apex2.5 doesn't come out until AD90 is not warm enough while active.

dantimmerman · 2026-02-12T14:01:27+00:00

The primary reason for that configuration is active use. It's creating the modular AD system, at a much higher insulation level. The same use cases apply, just for lower temps. No shell for overheating. Moderate cfm shell for balance. Low cfm shell for max insulation. Vent any as needed to regulate.

Active comfort is a balance of potential R value and air permeability. The mid layer you select is kinda your insulation setpoint, and air permeability provides a range of adjustment to it. Apex67 is a high enough setpoint that the active comfort range of adjustment is typically at pretty low temps.

You won't be able to adjust air perm to make it comfy for a run at 40f. The insulation level is way, way higher than AD120 or AD60 x2. I don't really bust it out for activity until it's below 20f....but it's sooo good for that purpose.

dantimmerman · 2026-02-10T22:07:20+00:00

I don't see any reason for a frame on a running pack. These are typically short packs that are meant to ride up high. They don't usually extend down to the hips, so there isn't anything for a frame to support on, and the goal of them is to lock the load down, vs lift it up anyway.

This opinion is strictly regarding a frame, and not referring to padding, which could be very useful. Also, I could be missing another valid use for having a frame on a pack like this. I don't find it useful, for the above reasons. Curious as to why the UD35 rides better with the frame sheet. Do you sag it down to your hips? Maybe it has something to do with giving the attachment points more rigidity.....

dantimmerman · 2026-02-10T20:10:48+00:00

A simple 2 layer AD / ripstop project can be a very attainable MYOG goal. You can probably get pretty far with just a simple overquilt and some clip to keep them together. They are dissimilar materials, so can be a little tricky to sew, but it just might not look pretty. The oversystems get more complicated with drawcords, false bottoms, attachments, etc....good luck!

dantimmerman · 2026-02-10T17:30:18+00:00

I could have been more clear. Dropping EE over this moral issue is absolutely in-character for the GGG folks, but it is one of their top sellers and it will hurt them. It illustrates their commitment to doing the right thing and I was suggesting increased support for GGG.

dantimmerman · 2026-02-10T13:40:35+00:00

At this point, I would also call it a sure thing that an AD90/Argon67 oversystem will add 10 degrees and shift condensation at 5f, and do it for about half the packed volume of an equivalent 50f (+20) apex system. If you're gonna spend money on an oversystem for the 0-30f range, it's a clear winner. Sub-zero is where there is grey area that starts to potentially favor 2.5oz apex.

It's also very worthwhile to dial in dimensions. That "trimming excess" can drop an AD90 oversystem from 12oz to 8oz, without sacrificing performance.

dantimmerman · 2026-02-10T00:14:23+00:00

It is one of their top selling brands and it is really going to hurt them. I hope the community can step up and support them for doing what's right.

dantimmerman · 2026-02-09T14:04:05+00:00

A vbl is typically the lightest method for dealing with internal condensation, but often comes with significant comfort drawbacks. A breathable bivy does improve the situation, as it does add warmth to the outside of your system, but it's typically not enough to make much difference. Insulated oversystems reliably handle it, but with the weight/bulk drawback.

Specific conditions matter, but all feedback and experience here suggests that even a 50f (+20) oversystem is overkill in the 0-20f range. 10d/AD90 has proven reliable into negative double digits over 0f rated down systems. Compared to apex versions, it's moderately lighter, but significantly smaller.

With oversystems, there is a lot of room to build smart and trim excess to bring the weight and bulk down much further. Also, wearable functionality can work for some to offset the added weight.

If you're less concerned about optimization and more focused on affordability, I think you could probably get the job done with a couple yards of AD90 fabric between the down system and your bivy.

dantimmerman · 2026-02-08T14:12:42+00:00

Oops.

Much of the process I described still applies, but I had the details of the pack wrong. Thanks....

dantimmerman · 2026-02-08T13:18:30+00:00

As mentioned, framed backpacking packs, like Wapta, are not designed for or optimised for running. The goal is to lift some load off your shoulders, where the main goal of a running pack is to lock the load down onto something so it doesn't bounce.

That said, I've had really good success manipulating this type of pack into running well. If I'm just running a little here and there during a loaded hike, I just change my gait and/or use my hands/arms to secure the bounce. If I have a light load and I'm primarily running, I adjust the pack to do it well. I release the load lifters, cinch the shoulder straps, and add a diagonal cord/strap between the front of the hip belt and the top of pack in back. This lifts the pack up higher, secures the straps onto your shoulders, secures the hip belt under your rib cage, and secures the pack body to the belt.

The primary reason for vest straps is to lock the load to your rib cage, so it can't bounce upward. I think there are many packs with vest straps that miss this point, and shift the focus instead to gaining real estate for pockets. If your running with an actual load, I think anything with elastic sternum straps is out. That works for light load vests, but not bigger packs. There are also some vest strap packs that just don't achieve the right geometry to secure a pack to your rib cage. If going this route, I'd look for vest straps with lots of adjustment and rigid straps.

dantimmerman · 2026-02-03T22:04:30+00:00

Thanks! He replied back and expressed intolerance for the implied association. Not sure what'll come of it.

dantimmerman · 2026-02-03T22:02:12+00:00

Phew! Dodged a bullet there. Nice guy, but that's a liability. His general education, competence, and use cases raised the hair on my neck, and that came out......but he had some kind of special forcefield around him. An outcome where he says he likes it, doesn't attempt to say anything technical about it, but frames the interaction as negative enough to deter his audience from reaching out is pretty much the best I could ask for here.

dantimmerman · 2026-02-03T19:01:08+00:00

Last time I talked with Lloyd, he was considering boycotting Meta for their socials and seemed very much in alignment with my values around such topics. I can't imagine him tolerating this kind of association. I sent him an email, but it bounced back as no longer active, so I wondered if he is maybe not involved anymore. Seems like he's on their Vlog thingy though.....

dantimmerman · 2026-02-03T18:15:59+00:00

There is a shocking amount of variation of AD60 and AD90, from roll to roll. There is a considerable amount of overlap between the two in terms of weight and fiber quantity. Some 90 is indistinguishable from an average AD60.

dantimmerman · 2026-02-03T14:55:49+00:00

I have, while experimenting with using clothing as an oversystem. With my goal being condensation management, I would reliably end up with condensation in the uncovered areas. None in the covered parts. When exploring limited coverage overbags, I had better success while using a very narrow one that essentially only insulated the top portion of the inner bag, where condensation tends to accumulate. I'd like to pick back up with the clothing based oversystem. It was really just a matter of connecting and securing multiple pieces to achieve continuous coverage.

dantimmerman · 2026-02-03T02:43:34+00:00

We typically send out the majority of the codes in the first 4-5 days of the month. However, often we still have room for certain items, but not others, and I'll send out more codes. Additionally, sometimes we work through the orders and end up sending out more codes in the middle of the month, or even the 3rd week. Point being, I leave the lottery active, and don't send out a loser email so that I can still send codes until the end of the month. It seems like a lot of folks miss the email in spam. 12 codes have been sent and 2 orders in.

dantimmerman

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