Condensation polymers baring cleavable groups such as esters and amides can also be completely depolymerised by hydrolysis or solvolysis. This can be a purely chemical process but may also be promoted by enzymes.  Such technologies are less well developed than those of thermal depolymerisation, but have the potential for lower energy costs. Thus far, polyethylene terephthalate has been the most heavily studied polymer. Alternatively, waste plastic may be converted into other valuable chemicals (not necessarily monomers) by microbial action.