A big bike messenger bag will not cover up your whole back, and prevent sweat from cooling you.
thus, I have tried to avoid wearing a backpack ,
In the winter it will matter less, of course..
In the rain , there are Dry Bag Backpacks ,
but there a Messenger bag with a waterproof liner may be OK.
....
Last edited by fietsbob; 08-09-18 at 10:07 AM.