rapidly and holds moisture. Not dries out...
Honestly I think that is the entire trick. Doesn't matter how you get there - there are lots of different components out there. I've grown slippers in everything, including semi-hydro, straight chunky peat (very hard to find) and peat based high porosity mixes (Promix HP, for example, but I'll add another 25% or so perlite). It freaks customers out though, so I mostly use bark mixes. Can grow them in marbles if you water twice a day.
My mix varies (I never measure, just mix what I have available until it feels right) but it is about 1/2 small bark, 1/4 sponge rock, 1/4 fleximix (which you can't buy anymore, I reserve it for phrags) - I'm using rockwool cubes now which is an inferior substitution - + a generous amount of oyster shell for the 2.25" pots. I use a similar mix but with medium bark and larger sponge rock for things that are bigger. I've used leca balls instead of the sponge roc before. I used to add a generous amount of charcoal but it has gotten hard to find recently.
Very important to let the mix hydrate for at least a day or two before using it. I often add a small amount of detergent to the mix. Helps the bark get wet faster. I will literally drown the mix, as much water as I can fit in the container and I put something heavy on top to keep it submerged. After a day or two I drain off the excess water.
Pro-tip. Aerate your water. Hard. As many bubbles as you can force through your water reservoir. I use a pond bubbler in my 1000 gallon rainwater tank that runs constantly. Try it.