What is "greenest" thread?

We compromised on thread today. For weeks we had been banging our heads against a wall. We were deliberating between 100% cotton thread, cotton wrapped polyester core thread, 100% polyester thread, and nylon thread. None of them were perfect. 

Our first inclination had been to go with cotton thread, organic if we could find it. Using cotton thread would allow us to maintain the biodegradability of the jeans at the end of its life, and would be more of a natural material. But organic cotton thread were only readily available in Tex sizes that were less than 30, suitable only for t-shirts and knits. Conventional cotton thread didn't come much larger than that, and the one Tex-90 thread that we were able to order, called "gassed cotton", ended up being closer to cotton string and would fray and snap in the machine. In general, cotton thread would prove to be weaker than any polyester thread, prone to wearing and breaking and compromising on the longevity of the garment. 

What about recycled polyester then? The big thread manufacturers Guetermann, Coats, and American & Efird did carry a recycled poly thread under different names. Guetermann (which is apparently now owned by American & Efird) produced a thread with the moniker rPET, available in their existing lines of Sew-All Thread and Mara 100. Unfortunately, the largest sizes available were Tex 30. Coats carried an ecoVerde thread, but only at Tex 35 and seemingly not readily available. American & Efird had a recycled poly thread called Wildcat Repreve, which also only went up to Tex 35, and an organic cotton thread called Anecot Organic which was available in Tex 70 and 105.

Unfortunately, there was no Anecot Organic currently available in the US. The A&E representative told me that the organic thread was produced in India, and due to lack of demand, could only be made to order, with extremely high minimums. Furthermore,  they would not be able to organically dye the thread. As we ended the conversation, he added, "You know, we also carry a 100% cotton thread, which is produced in the US with a long staple fiber and, though it's not organic, it is 100% cotton. A lot of customers who come to us initially asking about the organic thread end up purchasing just the cotton thread because they realize the organic stuff is prohibitively expensive and it doesn't come in any colors." Another blow to the sustainability entrepreneurs.  

With the need to start pushing out product, we decided on purchasing A&E D-Core thread that another company had in overstock, so that at least we were helping to reduce the burden of waste rather than produce virgin material.  D-Core is one of the best options out there for denim, as it is a cotton wrapped thread with a poly core. The core adds strength and resilience to the thread while the cotton adds natural fade and softness to the surface. Combining the two worlds, this thread is one of the most often used threads in the premium denim market. 

Nevertheless, we aspire to find a thread supplier whose materials are 100% biodegradable, with the tensile strength to take on all that we put our jeans through.