On berries 40% would work here. But we have lots of sun. I'd go 50% here on blackberries but maybe not on blueberries although I think that would work well. May around here are growing all sorts of things under two layers of the weed barrier. And that's all yr long.

The woven 30% black polypropylene is very strong, lasts a long time in the sun, is about as cheap as any, and is smooth so doesn't snag or tangle. Woven comes in higher shade levels.

On blackberries I'd use 50% here just to lower the light/heat stress that causes sunburned small fruit. 40% should work for you.

The Fruitnut

I've been using some inexpensive stuff my wife bought. It is black and similar to the white woven nylon bags you use to put soil and fine rock items in when you shop at a landscape supply. It is quite opaque, certainly more than 50% shading.

Once caneberry fruits show any color past the green stage, it doesn't matter how shaded they are, you could put them under a cardboard box and they would ripen, of course the airflow would be a problem!

Your shadecloth should be a tight weave with no tangling or snaring problems at all. Use clothespins to attach to canes/fruiting spurs.