I have a crafting question. I have polyester oxford cloth banners I want to paint stenciled letters onto using acrylic paint, and I'm wondering if I can just paint on it without treating the cloth, or if I should set the cloth by sizing it in some fabric glue & hot water (1:1) and air dry it a couple days, like you would, for prepping a canvas for painting? Since I'd be rolling up the banner and using it over and over once painted, I'm wondering if treating the fabric this way would help with durability as well as making the paint adhere better. Pic is just an example of what my banner looks like. TIA #asknostr #crafts 
Discussion
why not mix fabric medium into your acrylic paint?
I don't know if putting sizing on the banner would be good if you're going to be manipulating the fabric a lot because it might start to crack. canvases are pretty much never folded so a sizing/base coat works for them.
I'd probably also seal it after it's painted with a clear coat. I'd imagine if this banner is hanging out in sunlight a lot, it'll get a fair amount of UV damage. maybe like what they use for outdoor furniture.
The banner is pretty big and the lettering will be too, so it's very visible from the street if I hang it as part of my backdrop (which is inside my tent, and in the shade). Only in desperation would I hang it outside. But if I decide to do that, would that be an acrylic clear coat?
yeah, I'd spray it instead of painting it on though. you want it to be thin so it can stay flexible. maybe there's an acrylic clear coat made for fabrics?
Probably good idea to prevent flaking of the paint. I suppose acrylic will stay flexible on the polyester cloth when rolling it up over and over? I wouldn't want to fold it after painting, because it's always got creases that way.
the fabric medium is what makes the acrylic paint more flexible so it doesn't flake or crack.
your best bet is to do some testing samples. I haven't done a banner like this myself so that's what I'd do first.
I'm... Not cloth savy, but I do know plastics pretty well. PE is a pain to paint without some kind of nasty stuff in the pigment carrier. I'm not sure most paints are going to want to stick-well enough long term.
I'd definitely get a cardboard tube and roll it instead of folding it to prevent the paint from cracking on joints.
I think I have solved this. Thanks for all your help