Milk Soap Showdown
A while ago, I decided to find out how different milks will perform in soap. The experiment used the same oils and lye for every batch, with no additives, so the only difference between them was the type of milk used as 100% of the fluid. I made a test batch out of every kind of milk I could get my curious hands on. And now it's time to put them to the test!
To be as objective as possible I decided to line them up in alphabetical order. Let's see how they compare.

Almond milk: Bubbles into a buildable lather with a nice slippery feel. Fairly long lasting. My hands feel really soft and smooth after.

Banana milk: Smaller bubble. Takes a bit of effort to work up a lather which has an interesting, almost slimy, viscosity. After rinsing, my hands felt almost slightly tacky. Once dry, my skin feels suuuper soft.

Cashew milk: This one gave a light, almost dry feeling, frothy lather that was buildable. My skin feels nice and not like there's anything sitting on it that needs a minute to absorb.

Coconut milk: Fairly fluffy big bubbles, and with rubbing my hands together, the lather became dense and almost lotion like. After rinsing, my skin feels a little slick. Once dry and given a minute to absorb, soft.

Cow milk: Modest lather. After rinsing, it has a similar to coconut emollient feeling left on my skin that absorbs leaving a smooth and soft moisturized feeling.

Flax milk: Another nice but modest lather. This one has a slightly viscous feel but much less slimy than banana. Also not as moisturizing on the skin.

Goat milk: Okay this one surprised me a bit. The bubbles are so small! This is a different blend of oils that I use for my bars of Goat Milk soap, and wow it makes a difference. The lather was meh, but did have a lotion like feel across my hand, and left my skin very soft, but not as moisturized as I expected.

Oat milk: This one wasn't quick to bubble, but made for a nice lather with a silky feel that built into a dense foam. After rinsing there's no slick or tacky feel, yet my skin feels soft.

Pistachio milk: This is one bubbles up readily and makes nice bubbles. after rinsing I do have a slightly slick feeling on my skin that absorbs readily and leaves skin feeling fairly smooth.

Rice milk: I was very curious how this one would do since as a milk it was thin, almost watery compared to all the others, and it was a pleasant surprise. Bubbles readily and with an interesting mix of dense and big bubbles. The lather was both buildable and long lasting with lightweight feel. After rinsing my skin feels really nice and soft.

Soy milk: Nice lather with good bubbles. My skin feels pretty nice after, nothing too remarkable.

Walnut milk: A creamy, dense lather. It doesn't work up big bubbles, but instead gets dense and lotion like. Very similar to how coconut milk and goat milk performed. After rising, my hands feel moisturized and smooth.
The biggest surprise- Biggest happy surprise Rice milk. Biggest unhappy surprise Goat milk really underwhelmed me.
The worst of the bunch- Probably Banana milk. That was such an odd texture, it wasn't exactly pleasant. However my skin felt fantastic after letting that leftover tacky feel absorb in.
Overall- I think it depends of what you are wanting to add to the soap. Some seem to boost bubbles, while others bring extra emollients for a more moisturizing skin feel.
Going forward I definitely see myself using some of these plant milks more! Especially playing with ratios and combinations. I foresee a Cashew and Banana combo perhaps to get the skin smoothing properties from one, and the light fluffy bubbles from the other and see how they work together in a batch.
More experiments ahead!