This is a super tailored Ben Zuckerman suit in a brown glen plaid. Glen plaid (short for Glen Urquhart plaid) or Glenurquhart check is a woollen fabric with a woven twill design of small and large checks. It is usually made of black/grey and white, or with more muted colours, particularly with two dark and two light stripes alternate with four dark and four light stripes which creates a crossing pattern of irregular checks.

Photos courtesy of Frock It To Me Vintage.