What do the sizes mean when describing a plastic bag?
You will see plastic bags defined by the size and the thickness (see gauge):
1. If two sizes are defined, e.g. 20 x 30 this means the bag is 20 inches wide and 30 inches long. These sizes are when the bag is laid flat.
2. If three sizes are defined e.g. 18 x 29 x 39 this means the bag has a gusset - i.e. it is tapered in at the bottom. A gusset is useful when using the bag as a bin liner as it folds the excess polythene into the bottom of the bag. The first dimension is the width at the bottom, therefore in this example the bag would be:
18 inches = width at the bottom
29 inches = width at the top
39 inches = length of the bag
Polythene bags are made as a tube and then cut to length. Having a non-standard length is therefore relatively easy to achieve. Having a non-standard width generally requires moulding the polythene to this width, which will have a minimum quantity, typically of 0.5T of polythene.