Aquascape Geotextile Felt Underlayment
Underlay is sold by the running foot and comes in 7.5ft and 12.5ft widths. When purchasing, simply enter the number of running feet you need in the "quantity" field (e.g. if you need 12.5ft x 10ft, choose the 12.5ft for width and type "10" as the quantity).
Additionally, the 12.5ft underlay comes in a 6oz and 8oz weight. The 8oz is heavier.