US Patent 11937707 Chair with a flexible backrest

A chair having a backrest having an upper backrest section and a lumbar section, wherein the lumbar section is provided with a plurality of perforations and is elastically deformable to allow a backward tilting movement of the upper backrest section under a backward thrust applied from a user's back, and wherein the perforations stop the backward tilting movement of the upper backrest section in a position of maximum backward tilt of the upper backrest section.