Hi steelwindmachine,
While it’s impossible to cover the properties of every possible pillow or pillow material on the market because there are so many (memory foam, polyfoam, latex, shredded foam materials, different types of wool or other animal fibers, plant fibers such as kapok or cotton, feathers, down, synthetic fibers or fiber “clusters”, buckwheat or millet hulls, and others) … in very general terms fiber fillings will tend to compress and pack down and become firmer over time (or in some cases over the course of the night) more than foam materials or shredded foam materials. Wool is one of the stronger and more resilient fibers though so it tends to maintain its loft better and for longer than other fibers such as polyester (dacron) or cotton (especially wool “balls” vs wool batting) .
On the other hand … fiber materials in either a pillow stuffing or in a pillow casing (in particular natural fibers) also tend to be more breathable, moisture wicking and temperature regulating than foam materials (particularly memory foam).
Some of the many variables that are involved with temperature regulation for mattresses are discussed in post #2 here and these would apply to pillows as well. The type of fabric used in the pillow casing is also right next to your skin and can also affect moisture and temperature regulation as well.
A suitable pillow is an essential part of good alignment for the head and neck and upper body because the gap between the head and the mattress and the curve of the cervical spine needs to be supported just like all other parts of the spine. Like mattresses … there are certain “needs” that depend on body type and sleeping positions but with pillows, personal preferences play a more important role because the face is much more sensitive to textures, temperature, smells, and other more subjective “feel” based properties of a pillow. There is more about choosing pillows in the pillow thread here and the other topics and sources of information that it links to that may be helpful as well.
Better sleep shops will often have samples of their pillows available for you to try (they should be in a pillowcase and not a plastic wrapping) so you can try different types of pillows and pillow materials in person and use your own personal experience rather than just “theory” to help you decide on the types of pillows and pillow stuffing you tend to prefer.
Phoenix