Firestone PondGuard EPDM rubber liners are the industry standard when it comes to EPDM pond liners. PondGuard is made especially for ponds and water gardens with no algaecides or fire retardants like found in most EPDM roofing liners. PondGuard is guaranteed not leach any harmful chemicals into your pond like some cheaper liners. In addition, the liner is very UV resistant, and no covering of the liner is required below water level if desired.
The main advantage of EPDM in general is it's flexibility. If your pond has many corners, bends or shelves, EPDM is able to bend and fold to pretty much any shape. It is also quite temperature and weather resistant, tested to withstand temperatures as cold as -40 degrees Fahrenheit and as hot as 175.
Firestone guarantees the PondGuard EPDM rubber liners for 20 years as long as the liner is installed as per manufacturer recommendations. One such recommendation is the use of an appropriate underlay underneath the liner to help increase the puncture resistance of the liner. To see the underlay we recommend and sell for Firestone PondGuard, please see the page here.
The main advantage of EPDM is it is very flexible. Even though RPE liners are stronger and lighter, EPDM is much more pliable making it easier to conform to ponds with lots of bends and tight corners.
Despite being more flexible, EPDM is much heavier than RPE's making it more expensive to ship and harder to lift when installing. In addition, EPDM isn't quite as strong or puncture resistant as RPE, which means that an underlay is needed more often which brings up the price a bit. Since EPDM rubber is softer and thus less puncture resistant, it is easier to damage with sharp objects in the substrate below the liner. Because EPDM is quite a bit heavier than RPE, EPDM often isn't available in as large of single panels as RPE, which will mean seaming the liner together on site in larger applications. All that being said, EPDM is still a great choice in small to medium sized applications as long as care is taken to not damage the liner.