(a) The ply fibres shall consist only of polyester materials as detailed in the Mainsail Sailcloth Appendix.

(c) Sail reinforcement shall comply with Mainsail Sailcloth Appendix.

Black and white. If it is not on the list it is illegal. Does not matter how cheap or expensive, fast or slow it is.

If a sail maker wants to build and F18 sail and supply it to a customer as one, they need to understand the rules from measurment to material specs.

If a class measurer is measuring in the sails, he needs to also understand and follow these rules.

If a sail cloth provider wants their material to be elegibale for F18 sail production, they must seek approval from the F18 class.

Do you really need to make it even more simple than this?