I got more information on polyester as a hydroponic material. Turns out that STG is made of polyester. A few things to consider with it is that it is not moisture wicking and will completely drain. So it is good for constant feed systems. (I experienced this personally, when one of my lettuce plants wilted and found that they polyester was not obsorbing the water and pulling up to the roots.) So a water introduction directly to the polyester is a good thing. I also have mine running at a constant cycle, so the water never stops running to the roots.
This seems to be a less known
growing medium, but there are a few articals on it. It is non reactive, neutral, and safe. (you drink from polyester every time you have a drink in a plastic bottle. Soda and water bottles are often made from the same plastics that make polyester.)
The STG cubes I am using are working well. Most of my plant issues are self inflicted. (I am too nosey) You just have to remember to make sure your watering system will be able to provide adiquate watering to your plants, as the polyester is hydrophobic, and will not obsorbe the water directly, but will hold a little for a short time in the small pockets between the fibers.