What are wetting agents and which function do they fulfill?

Wetting agents are ionic or anionic surfactants which increase the surface tension of water. Since peat and peat-based substrates react water-repellently as of a certain drying degree, a wetting agent, that is not harmful to plants, can be added to the substrate. In general, it is a mixture of ionic and non-ionic surfactants which decompose biologically during the course of cultivation.