This Kaj chair is often incorrectly attributed to Swedish furniture designer Karl Malmsten. In fact it was designed by Karl's son, Vidar Malmsten, who was trained as an interior architect.
Designed in 1959, the chair's two seat material options were wicker or leather. The leather seat option contains a primitive, if workable, means of adjusting the tautness when the leather starts to stretch:
The chair, by the way, is stackable.
It's still in production today, by Swedish furniture manufacturer Tre Sekel.
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