Flexibility is more related to the gauge of the individual strands of wire that make up the total wire. IOW a cheap wire will have very few strands but each strand will be thick, a better more flexible option would be very fine strands but very many of them. Of course if you live in colder climates like mine, the material of the jacket makes a big difference. A more rubbery jacked will remain flexible even in sub zero(F) temps while a vinyl or plasticy jacket will start getting stiff as it gets below about 40f and become basically worthless below zero F.
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a