Bare leather is (or should be) the final step in stropping. The reason being that the natural silicates found in ALL leather (and carbon-based life forms including all plants and animals) are the smallest particle size found naturally. True, there are polishing films available that give a smaller grit, but they are not commonly sold as sharpening abrasives, rather polishing compounds, and usually quite expensive.
Horsehide and kangaroo hide have the highest level of natural silicates per square millimeter, followed by grass-fed cowhide. But don't be led down the garden path by the numbers. All it means is that if you have to take 20 strokes on cowhide to produce a result, you'll only need 19 strokes on horsehide or kangaroo. Keep in mind that this is the difference in the amount of silicates found. The natural density of the various leathers also plays a part in the results, which is why horsehide has been the 'go to' strop material for bare leather strops for hundreds of years. It's the combination of natural silicates and extreme density of cell structure that makes it perfect for 'final' stropping.
Stitchawl