When installing a pond it is important to lay an underlay first. This is especially true when building a pond on rough or stoney ground. A pond liner underlay needs to be a geotextile. A geotextile has the following qualities:

Permeable  ie, lets water pass through it

A fabric intended to be laid against the soil

Has the ability to separate, filter, reinforce, protect or drain

Geotextiles are used in a whole host of situations. For instance they can be used as a protective layer in landfill sites or used to assist stability under railway tracks. However, of course, they can also be used to protect pond liners. Pond liner underlay will typically be made up from man-made fabrics such as polyester or polypropylene. One of the key strengths of such 

man-made fabrics is that they will not rot down when exposed to the earth for a long length of time. This is one of the problems when non geotextiles such as old carpet is used to line a pond. If the carpet is made from a natural fibre such as wool it will reduce in thickness over time allowing any sharp stones to protrude and potentially puncture the pond liner above.

The form of the geotextile fabric will typically be needle punched, heat bonded or woven. Our bestselling pond fleece pond liner underlay is a needle punched fabric - this process adds 'air' to the fabric giving it terrific cushioning properties. A lot of effort goes into building a pond and it is always worth going 'the extra yard' and installing a pond liner underlay. There is nothing more disappointing than digging a hole, preparing the ground, laying the pond liner then filling with water only to see from above rough points in the ground pushing into the fabric creating straining points that may puncture over time.