The fabric appears to be a premium blend (likely a high-grade wool, suiting blend, or tropical fabric) that offers a crisp drape and excellent structure, ideal for a waistcoat that needs to hold its form. The finish has a slight sheen, indicating quality and giving the waistcoat a luxurious, polished look.

This is an excellent choice for a blazer that can be paired with solid suits for a modern flair, or worn separately with trousers for a smart-casual ensemble."