Cat runs should be made from welded wire mesh with a hole size of 25mm.
The standard 1.5 mm wire is used extensively for domestic garden cat runs and pens. The 15 gauge (1.8mm wire) is slightly heavier to make an even stronger run. This is the mesh we often supply to catteries and cat rescues for commercial runs. The wire and electro-galvanized before welding giving it a smooth safe finish.
The HDPE hi-tensile plastic mesh is used for protecting the perimeter of a garden. It needs to be angled inwards at the top to prevent cats climbing over the top.