I've been keeping track of the soaps I use (mostly non-tallow now) and what the ingredients are and whether there are any common denominator ingredients to the soaps that work best for me. Most important is soaps that leave my face feeling good, not dry, without any irritation or razor burn. Also important is quality and duration of lather, slickness, and feel during the shave. Soaps have included Nuavia, Grooming Department, Holy Black, WSP Rustic, Caties, Siliski, SV, Route 66, Wickham, Soap Commander, Sudsy Soapery, Haslinger, SMN, Razorock, Dr. Jon's. After this very non-scientific study, I've decided that the key ingredient for me, for my skin, is shea butter. That is to say, every time my skin has felt particularly good, non-irritated after a shave without any razor burn or the like, it's been after I've used a high quality soap that has shea butter in it - Nuavia, Soap Commander, WSP Rustic, Siliski. Not the conventional wisdom, and each person is different, but this is what is happening for me, and those are the soaps that have risen to my top tier. Except for Siliski, they all have very simple and short lists of ingredients, but the shea butter seems to make the difference. It could be just a coincidence, but I'm choosing not to think so for the time being. (Maybe it will help me buy fewer soaps.) I wonder if anyone else has an ingredient that they feel this way about?