It is a fully vulcanised material. Not glued - which does not last.It is completely non-toxic. You do not take the risks associated with EPDM material which may be toxic. Many materials compare themselves with Butyl and may claim some better characteristics, but this is normally not true. Do not settle for second best to save a few pounds. Consider what your pond is actually costing. You do not want to rebuild it in a few years because of liner failure.