What does gauge mean when describing a polythene bag?

Gauge is the measurement of thickness of plastic bags. It is related to the SI measurement of microns as 1 micron = 4 gauge. Typical gauge sizes and microns equivalent are:

• 100 gauge = 25 microns = 0.025mm = Very light-weight, economy black bin liner typically sold in discount stores.
• 120 gauge = 30 microns = 0.03mm = Standard bin liner.
• 160 gauge = 40 microns = 0.04mm = General purpose, quality black bin liner for domestic kitchen waste.
• 200 gauge = 50 microns = 0.05mm = Heavy duty black bin liner - suitable for commercial kitchen waste.
• 300 gauge = 75 microns = 0.075mm = Heavy duty garden waste bag.
• 500 gauge = 125 microns = 0.125mm = Tough rubble sack - suitable for up to 40kg load.

Regardless of the thickness, sharp objects will puncture polythene (glass and metal). Thin bags will tear by pure weight or once punctured, however the thicker the bags will not tear easily without first being punctured.