Nylon and other synthetics are traditioanly not considered absorbant due tot he properties of each individual fiber. Each individual fiber is very smooth and texture is artificially produced. This makes it very difficult for water droplets/particles to adhere to.
plant fibers (cotton, bamboo etc) are again smooth but ghave mroe variation in their texture from the when the outer cells are layered. A bit of texture meens the water has a better chance of staying on.
Animal fibers (sheeps wool, alpaca etc) have a similar structure to human hair and have ‘scales’ or cuticles along their length. the ability of these cutlicles to move allows a lot of water to be trapped between them and therefor an animal fiber will hold the most water.
This instantly makes it more absorbant.
However, depending on how these fibers are spun into thread or yarn can also have an effect. IF the fibers are very tightly packed together then again there is less spaces (pockets) for water to be held, whereas more loosely spun yarns have pleanty of pockets between in fibre for water to be held, making them more absorbant.
Based on that 100% wool which is loosely spun would be most absorbant and a 100% man-made which is tightly spun would be the least abosrbant.
Somthing containig a blend of natural and man-made, especially if it has a spongy texture would not be hyper-absorbant but would still soak up enough water to be usefull.