Reiss's quality has declined precipitously over the past 3 years or so, which is a tremendous shame as they had some wonderful pieces around 2012 - 2019. They once used high quality materials on their outerwear and knits. In recent years, they're increasingly using polyester, rylon and other synthetic fabrics and decreasing the percentage of cotton or wool on most of their garments. They are still charging premium prices (~£300+ for coats) however the material composition of their products is nowhere near what it once was.
I would recommend avoiding purchasing full-price and trying clothes on in-store and checking labels before purchasing.