Preformed pond liners are a type of liners that are purchased in a pre-determined shape and size, and are often non-flexible. Unlike bulk flexible liners, which are able to adapt and fit to almost any pond, preformed liners are shaped during manufacturing and thus the dimensions and size of the liner cannot be changed on site.
One of the most talked about advantages of using a pre-shaped pond liner is that after installation, there will be no unsightly folds or pleats in the liner due to its custom shape. This is in contrast to flexible liners, which bunch up around corners and must be folded or pleated to make things look neat. In larger, deeper ponds this may not be a disadvantage since the liner can be hidden from view in many cases. Still, some people like the clean look of a rigid pond liner.
In the case of using fiberglass preformed pond liners, an important advantage is the ease of installation. Because fiberglass is quite rigid, the pond can be placed on the ground and filled with water straight away, with no other support necessary. This means that a fiberglass pond can be installed above ground, and then later hidden with landscaping. However, to be clear, this isn't the case with all preformed liners since plastic liners require full confinement in the ground to prevent cracking.
The main disadvantage of preformed pond liners is that once you buy a liner, your pond design is set in stone and can't be changed without purchasing a new liner. If you're the type of person who is good with planning, then this may not be a problem. However, like many other hobbies, pond keeping can slowly enthrall a person. Over time, you may desire a more advanced pond, such as a koi or goldfish pond. The problem with many rigid pond liners is that often times they are simply too shallow to properly control the water temperature for fish. If you do decide to go with a preformed pond liner, and would like to leave your options open for the future, try to get the deepest pond you can, with a volume of water in excess of 1000L since larger volumes of water react slower to temperature changes. However, that being said, you could always start small in the beginning and then build a second or adjoining pond later.
In general, there are three common materials available for preformed ponds: rigid plastic, fiberglass and flexible liner that is box-welded to create a certain shape. Plastic liners are less expensive than fiberglass liners or box-welded liners, but must be fully confined inside the ground to prevent the liner from flexing, and as a result, cracking. In contrast, fiberglass liners need no confinement whatsoever and can even remain freestanding on the ground while filled with water. Fiberglass liners are also much tougher than plastic liners, and can handle more abuse before damage and leaks will occur. However, as a downside, fiberglass is MUCH more expensive to buy and ship since they are heavy and large. A third option that won't crack like plastic, but is less expensive than fiberglass is a box-welded liner. Box-welding is the process of taking a flexible liner (we like polypropylene), and using heat welding equipment to melt multiple panels of liner together to create a shape. The advantage of our polypropylene is that is is strong, light and safe for fish, plants and human. A potential downside is that they are usually a variation of a rectangular or square shape. To learn more, please see the box-welded liner in store. To read more about either type of liner, please see our pages on fiberglass liners, plastic liners, or box-welded liners.
As an alternative to rigid pond liners, please see our page on flexible rubber liners.