Identify these chairs please  

Picked up 4 of these chairs earlier today in a charity store. Very good condition to the wood, the seats and back still in good condition even though show some wear, definitely the original straps. Interestingly each seat and back consist only of two straps - on the front and top the look perfectly perpendicular, on the back and underside the straps are on a slightly diagonal direction.
No tags, brands or labels whatsoever. Next to my Jens Risom chairs these appear very light, and also somewhat more elegant with the back legs pulled in somewhat under the seat.
Can anyone help me identify these chairs? I have looked through my design books but without success.....
Thank you!