The Semogue C7 Alchemy 1 is specifically marketed as a synth that can deal with hard soaps. In my opinion, for face lathering, you need to have robust skin. I sold mine as I personally didn‘t enjoy it for this purpose.
I have had many synthetics over the years and the only one still in my rotation is a Wald A1. It had not occurred to me to try it on a hard soap as I have badger brushes for that. But I actually don’t think it would have any difficulty creating a rich lather. A synthetic needs very little soap to perform. Maybe if the soap is bloomed for a few minutes prior to loading. I may try it out just to be sure.
Other synthetics to consider:
Plissoft noir; Omega Evo; Mühle XL
I have had many synthetics over the years and the only one still in my rotation is a Wald A1. It had not occurred to me to try it on a hard soap as I have badger brushes for that. But I actually don’t think it would have any difficulty creating a rich lather. A synthetic needs very little soap to perform. Maybe if the soap is bloomed for a few minutes prior to loading. I may try it out just to be sure.
Other synthetics to consider:
Plissoft noir; Omega Evo; Mühle XL