EPDM (ethylene propylene diene Monomer) is a synthetic rubber with properties very similar to butyl rubber pond liners. Historically butyl rubber pond liners have always been seen as ‘top of the tree’ in terms of desirability for pond builders. EPDM is a more modern fabric that takes all of the best elements of butyl pond liners onto a new level. It is black and textured just like butyl and when you put two samples together it is practically impossible to see or feel any difference. Our EPDM pond liners are 0.75mm thick. This is the standard thickness ? you can buy thicker pond liners but this makes the weight a real issue for what is only a marginal gain in strength. Plus thicker pond liners can leave bigger pleats when it is folded back on itself when installing into the corners of complex shapes. These pleats can retain water and get smelly and discolored over time.