An ebonite rod held in hand can be charged by rubbing

An ebonite rod held in hand can be charged by rubbing with flannel but a copper rod cannot be charged like this, why?

Both the human body and the copper rod conduct electricity. When it is attempted to charge a copper rod by rubbing, the charge flows from the rod to the earth through the hand. However, when ebonite rod is charged by rubbing, the charges so produced stay on the ebonite rod as it is a bad conductor of electricity.