We use exclusively 16AWG wire for power delivery on all of our 12VHPWR cables to comply with the official PCI-e specification. The sense wires, which are not responsible for power delivery, use 28AWG.
Please note that due to the increased thickness of 16AWG wire, our 12VHPWR cables only come in Pro variants. We are unable to make Classic 12VHPWR cables.