I just recieved this bag today.  It is heavy canvas and the top is ZIPPERED!  It is big but not too heavy.  I will be using this for my trip to the Philippines in a few weeks to carry two behemouth lenses for my camera...  a 150-500mm zoom lens and a 70-200mm f/2.8 lens... also two speedlights.  Yes, that is a lot of weight.  Since we're allowed to cary a personal bag along with a carry on (the rest of my Nikon D700 system.  It is NOT going to be fun carrying both bags from the ticket counter to the loading gate for my flight.  My camera bag has no wheels!