erg79

I use a pannier, but if I was forced to choose between a backpack and a messenger bag, I think I'd go for the messenger bag, for the reason of how it looks off the bike. I'd feel less like a dork walking around with a messenger bag than a backpack. My own opinion--not saying anyone who prefers a backpack looks dorky.

Freakin'Chickin

Yeah, I'll agree with most here: if I go to school or I plan of having a long day at one (or maybe two) place, then I'll choose a backpack. I don't have a locker so fiddling around with panniers is not a good option for me. I use my regular do-it-all bag, which is an Arcteryx Khamsin 38, that I use a lot, in the backcountry or around town. That way I know I can fit my books/gym clothes/lunches and I only have to strap it on and it's fine.

When I go to work ( I work part-time, which is at 3k from my house), or when I go to the cafe or library to study, or when I know I'll be in school only for one course, I grab my messenger bag. Less bulky, and as it is been said here, I really like it for running errands, as you can simply leave it on your shoulder, swivel it, load and go. Great for those bulky items that you forgot you needed to pick up before heading back home (2l milk carton, for example ). My bag is a Cocotte Equipement, a company from Mtl, PQ. And, it gets my back sweaty if I wear it close to my back. But, if I am only fiddling around town, grabbing an ice cream, doing as much walking as I am biking, I tend to let it hang a little lower. So less sweaty back. Still, I sweat profusely

WolfsBane

True messenger bags for cycling? Mission Works, Seagull, Bailey Works, R.E. Load, and PAC. Serious bags for the serious bike rider or commuter. Chrome makes for a nice carry bag.

ThermionicScott 

I've thought about running beads of that hobby gel stuff down the back of my backpack to promote air circulation (or at least keep much of the surface from directly contacting my back). Has anyone tried this?

I don't find backpacks containing about 10lbs of stuff to be too much of a hindrance, the sweat patch on my back when I arrive is my only complaint.

RGNY

Osprey Flapjack backpack and Timbuk2 (medium) messenger bag here.

messenger is sweatier, as the backpack has the stiff foam ridges that create (a little) airflow.

that said there is not a large difference.

gganio

I have tested out all possible solutions. I commute 12 miles one way and it is totally impossible for me to change at work. Neither it is acceptable the sweat patch. I like to use that ride to train myself for both road, track and mountain bike racing. That has slowly but surely increased the necessity to stop using panniers since that would have forced me to put racks on bikes where it is impossible to put racks. After several years of testing I have developed a ventilation cushion (modified from the one that I have on the seat of my recumbent bike) that does create this ventilation between the bag and the back and I am all set now. I normally use messenger bags with my road bikes because it is more aerodynamic . I change the swing side frequently not to get back pain. I use backpacks with the MTB because of stability. The trick not to sweat is ventilation. Riding a bike generates ventilation. If any of those bag companies would have built in ventilation air scoops on their bags, that would have helped a lot the users.
I am thinking of making several of my ventilation cushions and sell them on ebay.

acidfast7

i have a mess bag, day pack, rucksuck and some fine handmade italian bags.

i sweat with them all.

with the mess bag on my lower back
with the day pack on my lower/intermediate back with one edge touches
with the rucksack where the straps are ... this one has the best airflow
with the italian bag all over ... but it's really toned the leather to give it a nice color

mess bag (120€)



fjällräven rucksack (300€)



arc'teryx (90€)



campomaggi briefcase (450€)

mustang1

I've tried both. my messenger bag is a timbuk2 17" laptop holder. and I'm tellin ya, I LOVE this bag. it was pricey at £80 a few years ago. the only thing I dislike about it is a separate attachable strap which I never use (i should otherwise the bag keeps falling to the side but I kinda got used to it).

IDK how, but this bag never stays dirty. when I ride in rain, its covered in crap since I have no fenders. I swear, the next day the bag is clean. I guess the material they use makes the dirt fall off after it dries.

I like that it has clip belts rather than a zip. so much quicker to use, aids water proofness, and you don't need to worry about sips getting stuck (which has happened to everyone of my previous rucksacks).

There are a few pockets and compartments inside. I even tell my wife several times how much I love this bag. I love it so much that I've written several reviews on openvoids.blogspot.com. I intend on still having it 10th years down the line when I will gladly respond to another rucksack v messenger bag thread.