Correx sheeting prevents light from reaching the roots of your plants on an NFT table. Progrow supply Correx top-sheets as replacements for the complete GT range of NFT systems. To mark out your Correx top sheet simply evenly space your Rockwool cubes on the top-sheet, once you are happy with the position of your plants (remember that this will be the fixed position of your plants until they reach maturity, and so should be adequately spaced to prevent crowding.) mark around the Rockwool cube with a white marker, then cut out the cube on a hard wooden surface with a Stanley knife. All our Correx top-sheets are either black or silver and so guaranteed to be lightproof.