500 x large Grey Mailing Bags 400mm x 525mm + Lip (16 x 20.5), Qty 500 100% Opaque-100% Recyclable Our mailing bags and courier bags are made in a 3 layer extruded film. They have a permanent Peel and seal closure with high tear resistance. How to find the correct bag for the items you are despatching, firstly lay out your item and measure the long and short dimensions of it, and then check the sizes quoted in the Heading above are close to the size you need, The sizes quoted don’t include the flap. This film gives the bags strength and most importantly, makes the bag very opaque. We also get them made thicker than our competitors, The thickness of the film is 50mu or 200gauge, All of our Plastic postage bags are made from Strong Polythene LDPE, made from opaque Plastic in various colours.