I have a deMartini messenger bag, extra large.
Compared to some of the newer styles it is a large bag without the pockets and other doo-dads.
It can hold more than I can carry, have used it as a weekend bag. I put my laptop in a canvas sleeve
made to fit it, it is not padded. Any clothes or other items may help cushion it.
I'm a large moosey person, the extra large bag fits nicely across my back- the bag stays in place well.
Don't think i've ridden more than 20 km at one time with it, plenty comfortable. Have the strap adjusted so the bottom of the bag hangs nicely about my waistline. On a real warm humid day, feel some perspiration between the bag and my back. The bag taken a lot of abuse and keeps on going, it was
pouring rain this eve on the way home- bag was covered with road grime, just wiped the muck off when
i got home and hung it up to dry. everything on the inside was dry. It is a very nice bag for my needs and a great value.