It was interesting to see this capillary liner on the Garden.com website. It is sold as a replacement part for their "self-watering" patio planters. I'm guessing that the flap in the center is meant to be poked up through a drain hole.
I use polyester batting (or felt) material instead of capillary matting. It is one of the easiest ways to make sub-irrigated planters (SIPs). I call them aquapads.
Buy a bolt or a yard but buy some.
All container plant growers should have some of this material. It has excellent capillarity and is sustainable. Simply wash it in a diluted bleach solution. I do it all the time.
Photos of more ways to use it are on the way. Stay tuned.
Capillary Liner for Self Watering Baskets
Replacement capillary liner for use with the Self Watering Hanging Basket and the Self Watering Patio Planters. Available in 12" or 14"