People ask me about gauge more than almost anything else, and most of the confusion is not about the concept, it is about the units and the variation across the roll. Let me walk through it the way I explain it on the floor.
What gauge means and how it's measured
Gauge is just thickness. In the U.S. we measure it in mils, where one mil equals one thousandth of an inch. Outside the U.S. it is usually measured in microns, and the rough conversion is one mil to about 25.4 microns. We check gauge with a contact micrometer or an inline gauge measurement system that scans across the width as the film runs, because a single point reading at the center of the roll tells you almost nothing about the rest of the width.
Why gauge bands happen across the width
No blown film line holds perfectly uniform thickness across the entire layflat width. Small variations in die gap, air ring cooling, and resin flow create gauge bands, thin or thick stripes running down the length of the roll. A well-tuned line keeps that variation tight, but it never reaches zero. This is why we check gauge profile across the full width during production, not just at one spot, and why a customer's seal or strength complaint can sometimes be traced to a thin band rather than the film overall.
Why thicker isn't always the fix
When a customer has a strength complaint, the instinct is almost always to ask for thicker film. Sometimes that is the right call, but a lot of the time the real problem is which resin is doing the work, not how much of it there is. A film that is failing from puncture or impact may need a tougher resin blend, like a higher LLDPE or metallocene LLDPE fraction, rather than more mils of the same formulation. Adding gauge without fixing the resin mismatch just means you are paying for more material to fail the same way, slightly slower.
The short version
Gauge is thickness, measured in mils or microns, and it varies across the width even on a well-run line. Before you ask for thicker film to fix a strength problem, ask whether the resin blend is actually right for the failure mode you're seeing. Sometimes the fix is gauge. Often it isn't.