I've only made two layers thick so far, for a night stand. It's pretty strong and light as a feather.
I'm going to be making some tubes 4 layers thick then filling with expanding foam for my race car (holding my fuel cell). I'll be doing a three point flexural test to see the strength of that.
The awesome part is you can make the tube as strong as you need it by adding more layers (if dimensionally it is permitted).