Often this is a synthetic brown foam polymer, but glass wool and coco fibre have been used. Step 3 Placing the seed inside the soil. Chaff lining funnels the chaff and weed seeds into narrow rows behind the combine, where the residue is left to overwinter. Source: https://gigspeeddev.biz/2024/02/07/cannabis-cultivation-chronicles-a-seed-to-harvest-guide