Constructed using a knitted polyethylene mesh netting. Access to the bag is by top opening and is held shut with a drawstring. Also available for rich ocean usage. Colors vary according to mesh size, the 75cm, (1/32") bags are green, 1.5mm, (1/16") bags are red, 3mm, (1/8) bags are blue, and 2/7mm, (1/16"/1/4") are dark green. FS-B: spat collection bag. FS-BF: spat bag heavy fouling. 217mm for rich ocean usage.