Poly Nets are actually a plastic that is melted and then extruded into strands.
Those strands are then twisted, braided and or knotted into many uses including netting for many industries from sporting uses like volleyball, tennis, golf...plus baseball and softball of course...to uses in the fishing industry. Because it starts being formed as a liquid, it is easy to add color (black in most cases) as well as UV protection material...so each strand always stays black without fading AND the UV protection really lasts...giving you many seasons of use!
Being that it is a plastic, it will not absorb water or add unwanted weight to your cage frame.
It also weighs less than Nylon and may last longer in areas of real temperature swings and of course, in rainy parts of the country!
The downside of Poly is that it is a bit stiff and is not as easy to repair as nylon.
Best Price...for a very good material