Zephyr cloth is a thin kind of cassimere made in Belgium. The term also refers to a waterproof fabric of wool. The term may refer to a light wind called Zeffiro. The Zephyr is an extremely lightweight and breathable fabric with a square construction, made with an almost equal number of threads per centimeter in warp and weft. Its special weave allows an extraordinary breathability and works perfectly with square patterns.
That’s the right fabric if you’re looking for a shirt: