Four dining chairs model 69 designed by Alvar Aalto and manufactured by Artek in about 1933-1935. Unlike Thonet Alvar Aalto bended the wood not with steam, but by means the natural moisture of the Finnish Birch (sawing and water). A rare set that you are not see often anymore. Material birch. The seat height is 44.5 cm. Source: Book Alvar Aalto page 61.
These mid-century modern Alvar Aalto chairs are considering their age still in very good condition, some normal traces of use (see pictures).