Tinned copper braid for soldering 18605 or Molicel P45B INR21700 cells.
This copper braid offers better performance for LiIon cells compared to tin terminal ends or even silicone wire. You battery packs will have less heat buildup at the terminals giving better performance – higher possible amp drawer and less resistance buildup due to heat.

This video from Chris Rosser shows some test results form various battery packs including a custom build using  Molicel P45B INR21700 cells and compares the performance of each battery construction type.