Thats the silk screen material I am going to use to keep roots out of my drains. A long time hydro user on another forum says it the only thing that has worked for him. He says you may have to clean it off part way through a grow though.
I have some and thats one of the fabrics I used in that test above. It wicks a lot better than the ripstop nylon and flows water through itself very fast. BUT - the mesh size is much larger than the ripstop. I was thinking of using the silk screne instead of the ripstop, but the larger mesh size now has me worried a bit.
I have been re-reading Parkers membrane book and his patent application and some more details are starting to stick.
1) Apparently, even the ripstop nylon isnt 100% against roots. That makes me worry about the silk screen.
2) He is fanatical about the roots NOT sitting in water. He only wants the thinnest film of water on the roots, BUT you still need enough water.
3) Fresh air is critical.
He points out that a thin film of water will reach O2 saturation much much faster than a large body of water. The speed with which water reaches saturation, or the O2 absorption rate, is based primarily on surface area - all other factors being equal.
Lets say you have 1 cc of water with a 1 sq centimeter of surface area = 1cmx1cmx1cm. It will have some fixed rate at which it absorbs O2. Lets just say it takes 1 minute for that single cc of water to reach O2 saturation/equilibrium with the air in a given space.
If you take that same 1 cc of water and spread it out over a 10 sq centimeter area (1cmx10cmx .1cm thick), it will reach saturation 10 times faster. Spread it out over 100 centimeters of area (10cmx10cmx .01cm thick), and it will reach saturation 100 times faster.
His point is that a very very thin film of water on the roots, will absorb O2 and stay near the saturation point almost instantly - or at least stay saturated or close to saturated all the time - as long as there is fresh air in the root zone. That will allow the roots to take in O2 as fast as they need it.
So his main point is providing that very thin film of water along with fresh air on a constant basis. Any time the roots are sitting in more water than that thin film, they are not getting as much O2 as they could.
Even if the water is saturated by airstones, etc, it takes time for the O2 to move through a thicker layer of water. Longer than it takes for O2 in the air to enter a thin film and reach the roots.
That theory makes sense to me, but at the same time, I think maybe he is going a bit over board in minimizing the amount of water. At one point in the book, he talks about adding another barrier to keep roots out of the lower nute chamber, but then he pokes holes in that barrier to let more water through. He mentions that at those holes, the roots seem to grow faster than elsewhere. That seems to tell me that a little extra water is not bad.
Long story short - Im considering using the silk screen instead of the ripstop - but Im worried about root penetration into the nute chamber.....