Hi Jimmie,
Youâre right that wool can regulate temperatures in both directions so it would keep you in a more neutral temperature range rather than actually be âcoolingâ. This is why itâs used in desert environments (in thinner layers) as well as in arctic environments (in thicker layers).
There is more information about so called âbambooâ fabrics and other types of rayon/viscose fibers that are sourced from other cellulosic raw materials (such as beech trees or eucalyptus trees) in post #7 here and the posts it links to about sheets and bedding but the information there would apply to mattress covers as well.
Bamboo and other types of cellulosic fabrics are popular because it has good moisture wicking properties and have a soft and âsmoothâ hand feel as well.
Bamboo