The folded and extended length is:
hr = rip height
alpha = extended angle = 100 deg
tr = rip thickness = 1 mm
tf = fabric thickness = 0.3 mm
Lf= folded length per one = 2*hr*sin(alpha/2) = 2*14*sin(100)/2 = 21.4 mm
Rn= number of rib pairs = 170mm / 21.4mm = 8
Luf = unfolded length = Rn*(2*tr + 2*tf) = 8*(2*1 + 2*0.3) = 20.8 mm