Some bags have a gusset at the sides to help the bag open out more and enable a greater volume of items to be put in - a good example is a refuse sack.

A side gusset is expressed as a bag being x" wide opening to y" wide.

For example: if a refuse sack is 16" x 25" x 39" this means it is 16" wide opening to 25" wide when the gusset is opened, with a bag length of 39".

Others have a gusset at the bottom to enable a wide product to fit in - a good example is a carrier bag.

A bottom gusset is expressed as + x". For example: if a carrier bag is 15" x 18" + 3" then the carrier is 15" wide by 18" long with a bottom gusset of 3".