Grow towers are plastic towers with a polyester filter mat inside that acts as a support matrix for the plant roots. Water is pumped to the top of the tower where it can percolate down. The support matrix is made of polyester, similar to those used for filtering ponds. This is something that could be vert interesting to work with because if it lightweight, flexible, inexpensive, and durable.
I would be interested if we could also control the fiber orientation of the mats by fabricating them ourselves. This would allow us to control root density, percolation rates, and opacity of the mats/plants.