My head has around 40 (including some baby dreads at the front) and seems pretty full. There aren't many empty holes on the mask, and those are hidden underneath the back. Weight-wise it is ok. The dreads themselves don't add a whole lot to it, but when added to dread rings, a bio, and the mank itself, it gets pretty heavy!
But the foam lining fits snugly, so it feels ok. I reckon I could wear it for a good few hours if needs be (you know, say the length of a themed wedding in a castle for example)