A few questions about HMG packs…

Dunno about the hot weather stuff, but I carry groceries (oddly shaped, often firm items) in my HMG packs on a nearly daily basis. I definitely feel a poorly loaded batch of stuff poking me in the kidneys, shoulder blades, or other sensitive bits with some frequency. If you are carrying typical camping kit, this would be less of a concern than with hard objects like yogurt containers and 6 packs of beer. But you do need to pay a little attention to what is against your back. The larger Porter packs add a thin plastic framesheet, which helps a little. Smarter packing helps a lot.

I have had some random experiences with how the load pulls away from my back. Sometimes I can carry a huge weight and it rides nicely on my hips, and sometimes it kills my trapezius muscles. I have ended up adding load lifters and a taller frame to my 'bigger' HMG packs to make sure they never pull away from my back. My smaller pack is still stock. For the most part, like with the comments I made earlier, smart packing will get you the experience you desire.

Like Philip mentioned, it does get pokey. I'll fold up my air pad deflated and tuck it into the bladder holder to take the edge off items.

Not a fan of the back panel. Even in cool weather (40*F-50*F, Patagonia Houdini or Capilene 4), your back will end up sweaty since there's no breath-ability.

I have an HMG Windrider 2400. I don't think of it as finicky to load, but I don't put oddly shaped items against my back with any soft pack. I pay a little attention to load balancing by putting water bottles on opposite sides. Maximum weight I've carried in the Windrider is 33 pounds; if you plan to carry 40, you might see new problems.

The back is not breathable, not a problem for me wearing a light synthetic t-shirt in temperatures up to the low 80s F. But I sweat a lot backpacking in temperatures above 50 F, so YMMV. The waist padding is usually soaked in sweat after any significant climb at any temperature. I've never tried wearing this pack without a shirt.

— Rex

"1) How finicky are these packs when it comes to loading them? Are they easily put off balance? Is it easy to feel gear through the back panel? It was hard to tell from the ideal loading of soft weight bags in the store.

2) How comfortable is the non-breathable fabric back panel over time, especially in hot weather? Is sweating and clamminess a real issue here? Can you wear this pack comfortably without a shirt, or not a chance?"

I have used several HMG packs, with my current favorite the newest version Porter. They are not easily put off balance. In fact, the tall and narrow shape is ideal for off trail scrambling.

You will generate sweat against your back. You can either have a bowed suspension to permit airflow but which is neither ideal for carrying a load as it pushes the center of gravity away from your core or you can have a suspension that sucks the load to your back and becomes an extension of your movement. The HMG packs follow the second mantra.

Without a t-shirt? Never tried.

With respect to 'pointed' parts of the load being felt through the backpanel, I have never had this issue. However, I know how to pack a pack.

;)

Anyone have any idea why HMG just doesn't include either an integrated spacer mesh back panel or at least a sleeve to put in your own piece of foam? This would add maybe 2 ounces? The greatly added comfort seems like it would be more than worth the incremental weight gain.

Having totally non-breathable fabric right up against your back just seems like a bad design to me…

Having done some spring ski tours with my Porter recently where we got absolutely roasted by the sun and sweated buckets, I have to say I don't mind the HMG back panels. You will sweat against any back panel, no matter the design. I have used trampoline style packs a lot and don't find that my back stays dry with them, though there is a bit more of a cooling effect. And foam against your back is either a sponge (open cell) or functionally identical to what HMG has done (closed cell). You just can't win. With the HMG construction, there is virtually no water absorbed into the fabric so it dries in minutes. Just wear a really high quality wicking shirt like an Arc'x Motus T. Awesome shirt, awesome fabric.

I don't have any experience with backpacking in hot AND humid environs. That may be a different kettle of sweat.

+1,what Phillip said

I've been absolutely loving my HMG 4400 porter pack here in the sweltering, butter-thick humidity of Virginia. Packrafting throughout & deep in the woods + underbrush. Oh yeah, I even opted for the 150D black nylon for increased durability…AND heat retention!

Of course, loaded like this, I'd be lying if I said I did not get hot, but considering the materials + load bearing capabilities of the design I can't really ask for anything more. +1 on all comments re:wicking layers; that's really the only way to do it in humid/amphibious areas. Usually have dri-fit tank top Nike that's cool + minimal while preventing chaffing from straps + webbing. Compared to old school backpacks, the HMG does not trap air + condensation into the fabric/weave; I think this is why some older packs felt like they gained weight over time sitting around the Southern heat (well, hey, it happens to us all…)
Also, experience has confirmed to me that keeping proper fit+ kinesthetics are the priority (vs.ventilated backs displacing weight from core/axis) FWIW