I seated myself at the table and waited for Erik to reappear. When he did, he was in flawless evening attire: a tailcoat of Bath superfine, a black cravat, waistcoat of sapphire blue that was similar to the tone of my gown, beautifully fitted trousers, highly polished shoes and white kid gloves. I could not help my intake of breath at the mysterious, handsome creature before me, his porcelain mask somehow seeming both normal and natural. — Excerpt from In The Eye of The Beholder
Fabric is rather difficult to describe in writing. Luckily, a delightful site called Between a Gentleman and His Tailor laid out a basic description of Bath superfine for us. While the focus of the site is on Georgian/Regency attire, the fabric remains the same.
The double breasted tailcoat was based on a riding coat so it was short in front and divided in the rear to accommodate sitting a horse. It was made of a woolen broadcloth with a high warp and weft of fine threads or superfine.
A more detailed description comes from Our Everyday Life:
Superfine wool can be made from cashmere, merino and camel hair, and requires specific kinds of production techniques. It is used to make men’s and women’s suits, coats, jackets, sweaters and also blankets. As a result of the complex production required, it tends to be more expensive than other wool items. The fabrics made with superfine wool are usually very soft to the touch and long lasting if well cared for. This kind of wool provides warmth while being very lightweight.
Superfine suiting is still available at fabric stores or bespoke tailor shops today.