This soft fabric allows gas to escape. Protects your liner from sharp objects and spreads easily. Underlayment should cover all surfaces in which the liner will be placed - Underlayment does not require to be seamed, joints may be simply overlapped.

Sold by the sq.ft. in 10 foot widths.
Example:

10 x 10 = 100 sq.ft.

10 x 15 = 150 sq.ft.

10 x 20 = 200 sq.ft.