Two differences between the two - Hardwax oil contains only one type of solid, which is wax whereas Polywax oil contains waxes and resins, which provide a higher degree of protection and sealing. Hardwax oil is also completely natural, and therefore non-toxic. Polywax Oil uses a mixed base and therefore the mixing behaviour of that is a little unpredictable, whereas with hardwax oil you can mix with stains and other oil based materials.
