Very sturdy - which is a plus for puppies.  The panels are substantial but wish the wire posts were a little hefiter as they are already bent.  Turns out it is worth studying the panels to make sure they face the same direction when assembling the pen (if not the bottom edges are not flush to the ground/floor).  About to have a litter of puppies so I will be using both units that I purchased indoors and out so we will see how the pen holds up outside.