Abstract: A soil-less plant cultivation substrate, for use in hydroponic or aeroponic plant cultivation, adapts entangled layers of natural wool batting that has been chemically treated with a compound containing thiol to increase its water holding capacity. In the preferred embodiment, the chemical treatment uses thioglycolic acid, such as calcium thioglycolate or ammonium thioglycolate, to increase the wool's solubility and then a neutralizing agent, such as hydrogen peroxide, halts the process. The thiol compound reduces the disulfide bonds of cysteine in the cortex of the wool and the hydrogen peroxide neutralizes the reaction and oxidizes the cysteines back to cystine, although not all disulfide bonds are reformed. The addition of an alkaline modifier is used to moderate or hasten the breaking the disulfide bonds.