What is the ruling on the prayer of a person suffering from knee roughness (osteoarthritis) on an innovative prayer rug from "Myrest" that contains a "memory foam" layer to aid comfort?

There is no objection to praying on a medical prayer rug if it compresses under the worshipper's limbs, allowing him to firmly place his forehead on it during prostration, such that his head becomes stable on the ground or on what is connected to it. If it does not become stable, his prostration would be like prostrating in the air, and thus invalid, due to the saying of the Messenger of Allah, peace and blessings be upon him: "And when you prostrate, enable your forehead to reach the ground until you feel the solidity of the ground." This is what the jurists of all schools of thought have agreed upon. As for the knees, it is not obligatory to firmly place them.