It looks as though the Ortlieb bag would keep the back a bit cooler than a regular backpack. Some bags have a mesh backing that keeps the back cool as well.
I will report my experience with the Ortlieb Velocity when I get it.

i have the seal line urban backpack in small. i love it. the back ventilation is good (though not perfect- you need to have straps adjusted right so that the ventilation pad sits right on the upper portion of your back as you're leaning to reach your handlebars),it has lots of adjustable straps and the closure system is really clever, functional, and simple.

the inside is just one empty hole and the front pocket doesn't hold much so you might want to spring for their organizer pouch if you have a bunch of small stuff to carry.

i use it every day on my commute to work and it holds a pair of sneakers, jeans, shirt, gmat textbook, two u locks, a small tool bag, bike pump, trixie tool, and some other stuff. perfect size for daily use but now i kinda wish i got the large for those days when i have to haul a bunch of crap (the large is over 2x as big as the small however so i dunno if it'd be practical for daily use).

i have no stability problems when using the chest strap (never really need the waist strap), even when spinning down a large hill at 120rpms+

over the shoulder visibility is good- you get used to looking around your side more than over your shoulder (the top of the bag sometimes obstructs that view a little but not by much)

its also on sale at ems.com for right now something like 88$. ive gotten a lot of compliments on how the bag looks.

when shopping for a bag, i compared this to the waterproof ortlieb and the freight backpack. i chose the sealline because of price, simplicity (not so many straps everywhere), back ventilation (though the ortlieb has it too), the unique closure system (i like that there's no velcro involved) and cause i thought it looked the best.


edit-- if you're not planning on using this backpack while on a bike, the back ventilation won't work properly since your back will be making contact with the non-ventilated lower portion of the bag. hopefully this review will help someone looking for a bike-specific bag

hahahahahaha

this forum sucks.

I just picked up a second-hand R.E.Load backpack and it's a godsend. Huge, well made, burly as hell, and can be expanded/cinched down as needed. A bit strappy, but oh well.

When I don't need the huge size, I'll keep using my old Metropolis. When I can get away with even less, I'm all about my Mountainsmith lumbar pack. That little bag has proven itself worth its weight in gold.

I really like those little lumbar bags.
I bet it's comfortable too where it's positioned.

I'm hooked on two strap bags. I was all about messenger bags because I had never tried a good pack. I recommend packs to everyone now!

Definitely comfy. Great for work, biking, hiking, photography, etc. Some of the best money I've ever spent on anything, really. You'd be surprised how much it will comfortably hold, and Mountainsmith makes a pretty bulletproof product as well. Wholly recommended.

Soon I will have a bike bag for every occasion.

I love my ortleib

Black DIamond Covert, 22L.

I use it for everything from commuting to Backcountry skiing, it's one of the best packs I've ever used.

If it's an older reload backpack, be very careful with the outside pockets. They like to let things fall out.

Is it the veolcity or the messanger?

i just picked up a Sealline Urban backpack the small size. Its really a great bag it holds everything i could ever possibly want to carry with me while on a bike and room for some extra stuff if needed. The one HUGE pocket design does kind of suck but can easily be fixed with the organizer sleeve or making something yourself. I havent used it enough to give it a full review but i have taken it with me on a ride and it wasnt uncomfortable at all. It was packed with tools and everything and i barely felt the weight on my shoulders or back. My back did still get sweaty but really thats gunna happen no matter what when something is resting on your back or not. Overall im very pleased with it and glad i waited to find it for cheap. Ended up getting it off ebay brand new for 60 bucks.

Hope this helps.

Ive also looked at the Ortleib not sure if it was the velocity or messenger but they look really awesome and would probably have been my second choice.

velocity and the wierd thing is this is the only backpack where I don't have to organize things by weight to make it comfortable i simply throw things in and it feels stable and comfy

I would imagine the messenger wouldn't be much different

I picked up a chrome dully a couple weeks ago half off, which is why i jumped and got it. And I have loved it so far. It has plenty of space for me while commuting to work or on campus with school books. I'd recommend one.

I have an Overboard Waterproof Backpack. its 25 liters with a roll top, and i love it. its good for going to school, the store, or something like boating. obviously its good in the rain. it has large thick shoulder pads which are comfy. it also has chest and waist straps. here is a link for it, but if you look for more then two seconds you can find it for way cheaper. they also make it in a 20L and in different colors, although i prefer black everything.

https://www.thewaterproofstore.com/ob1014blk.html

Where'd you pick it up?

I've been searching for the perfect backpack as well. I decided on a Bagaboo workhorse. All the backpacks I wore had serious blindspots, and I wasn't sure I was ok with that. Obviously when you have a large load, 2 straps are better than 1, but often may not be necessary. The workhorse has a strap that can swing around and act as a 2nd strap similar to a backpack.

I'm not a messenger, nor do I ride any sort of ss/fg/track bikes but I live car free (in Atlanta) and a good pack is very important to me. I just got it a while ago, and I think I'll post a review on it. I was originally trying to decide between a seagull or a reload backpack but ended up with the bagaboo outta left field. There's just not that much info out there on any of these bags, especially the much less popular backpacks, so I thought it may be valuable to post a concise review. I know a lot of you folks live in places with a lot of cyclists, but here we are few and far between, and finding one of these bags to try on is a pain.

Glad to hear it.
I should be getting mine soon. It seems to be a decent size.