Most film spec sheets pack a dozen or more measurements onto a single page, and it is easy to either ignore them entirely or get lost trying to evaluate all of them at once. In practice, a handful of values do most of the work of predicting how a film will behave on your equipment and in your application.
Gauge and gauge tolerance
Gauge is the film's thickness, usually given in mils or microns. The nominal number matters less than the tolerance band around it. A film spec'd at 2.0 mil plus or minus 10% can run noticeably thinner in spots than one spec'd at 2.0 mil plus or minus 5%, and that variation is where seal failures and breaks tend to originate.
Tensile strength and elongation
Tensile strength tells you how much force the film resists before breaking, measured separately in the machine direction and cross direction. Elongation tells you how much the film stretches before that break happens. A film with high tensile strength but low elongation can still fail under sudden impact, because it has no give. Look at both numbers together, not tensile strength alone.
Dart impact and tear strength
Dart impact strength measures resistance to a sudden puncture, which correlates well with real-world drop and handling performance. Tear strength, usually reported as Elmendorf tear, measures how easily a tear propagates once it starts. A film can have excellent puncture resistance and still tear easily once a nick forms at an edge, so both numbers matter for different failure modes.
Seal strength and seal initiation temperature
Seal strength tells you how strong a seal is once formed. Seal initiation temperature tells you the minimum temperature at which the film begins forming a usable seal at all. On a high-speed form-fill-seal line, a film with a higher seal initiation temperature may force you to slow the line down or risk weak seals, regardless of how strong the seal strength number looks on paper.
Coefficient of friction and optical properties
Coefficient of friction, or COF, affects how the film feeds through equipment and how bags behave on a shelf or in a stack. Too low and bags slide uncontrollably; too high and they jam in feeding equipment. Optical properties like haze and gloss matter most for retail-facing applications where shelf appeal is part of the spec.
Reading the sheet as a system
No single number on a spec sheet tells the full story. A film that excels in one column can underperform in another, and the right combination depends entirely on what your application has to survive. Treat the spec sheet as a set of tradeoffs to weigh against your actual use case, not a scorecard to maximize.