PET Fiber
Polyethylene terephthalate (PET) is a relatively new arrival on the hydroponics scene. You are probably familiar with PET, even though you may not recognize it by name. PET is used to fabricate food containers (especially microwavable ones) and is commonly used as a batting for stuffing pillows. The development of PET as a hydroponics substrate was carried out primarily by the Dupont Corporation, who patented the technology in the late 90’s. Subsequently, the worldwide rights to manufacture and distribute it was licensed by Sure To Grow (which is also the trade name of the product - STG for short), a subsidiary of 6062 Holdings, LLC, based in Beachwood, Ohio.
STG is biologically inert and provided sterile from the manufacturer. Unlike rockwool, it is non-wicking (although a wicking formulation is under development) and will only draw water up to a height of about two inches. This keeps the root region moist while allowing the top to remain dry, thus discouraging surface algal growth. The material is hydrophilic and stores water in between the network of PET fibers from which it is made. When fully saturated it retains 25 per cent of its volume as air space. STG is very light and compressible so it can be shipped for relatively low cost. Probably only rice hulls can compete with it in this regard. STG is provided in standard shapes (1.5 and four inch cubes) as well as in sheets and as loose fill, so it can be used in any application where rockwool is used.
Figure 2. A relatively new product, PET is provided in forms designed to make it a direct substitute for rockwool. As shown here it comes as loose fill, as flat sheets and in cubes.
The low weight and flexibility of STG make it easy to work with. The sheets can simply be rolled up and disposed of, and although it is non-biodegradable, it doesn’t take up a lot of landfill space since it is so compressible.
Despite its many advantages (low weight, good wetting and aeration, inertness and biocompatibility, no affect on solution pH), it does have a couple of drawbacks. From a horticultural perspective, since it is non-wicking, directly sown seeds will likely require top watering to keep the moisture up. This could increase the amount of labor needed to start a crop. However, once the roots penetrate to the water level, top watering is no longer needed. As mentioned, PET is non-biodegradable and although it can be reused in theory, most growers choose to dispose of it rather than try to clean and reuse it. It has been shown to burn cleanly in incinerators so it has potential use as a fuel to avoid landfill deposition. PET is recyclable and can be used to make new packages, cosmetics, carpet, pillow fillings and fabrics. That said, most PET used in hydroponics is not recycled unless it is filtered from the waste stream by waste processors.