Flexible Packaging & Film Extrusion Glossary

Plain-language definitions for the terms that come up most often in blown film extrusion, packaging materials, and film testing. Built so a packaging buyer, not just a process engineer, can use it.

A

Anti-Block Additives

Fine particle additives blended into film resin that create microscopic surface roughness, preventing layers of film from sticking together on the roll.

B

Barrier Film

Film engineered to slow the passage of oxygen, moisture, or other gases, protecting the freshness, shelf life, or quality of what's inside the package.

Blown Film Extrusion

A manufacturing process that melts plastic resin and inflates it into a continuous tube of thin film, like blowing a giant bubble of molten plastic.

Bubble

The inflated tube of molten plastic formed above a blown film die, which cools and collapses into the flat rolls of film customers receive.

C

Cast Film

A film extrusion process where molten plastic is spread flat through a slot die directly onto a chilled roller, instead of being blown into a bubble.

Coefficient of Friction

A numerical measure of how easily one film surface slides against another or against a machine part, tested using ASTM D1894.

Coextrusion

A process that combines two or more different molten resins into a single film structure with distinct layers, each contributing a specific property.

Corona Treatment

An in-line surface treatment that uses electrical discharge to raise a film's surface energy, improving how well ink, adhesive, or coating sticks to it.

D

Dart Impact Strength

A standardized test measuring how much energy a film can absorb before a free-falling weighted dart punches through it, reported as a single weight value.

Die Gap

The narrow opening between the inner and outer rings of a blown film die, where molten plastic is forced out to begin forming the bubble.

E

EVOH (Ethylene Vinyl Alcohol)

A specialty resin that delivers one of the best oxygen barriers available in flexible packaging, used as a thin internal layer in coextruded films.

G

Gauge

The thickness of a film, most often measured in mils (thousandths of an inch) or microns, and one of the most basic specifications on any film order.

Gusseting

A process of folding the sides of a blown film tube inward before winding, so the finished bag expands outward into a flat-bottomed or box-like shape.

H

HDPE (High-Density Polyethylene)

A dense, highly linear, crystalline form of polyethylene known for stiffness, a crinkly feel, and strong moisture barrier properties in film.

L

LDPE (Low-Density Polyethylene)

A flexible, clear, low-density form of polyethylene made through high-pressure polymerization, known for its softness, sealability, and clarity.

LLDPE (Linear Low-Density Polyethylene)

A polyethylene resin made by copolymerizing ethylene with an alpha-olefin comonomer, prized for its strength, toughness, and stretch in film applications.

Layflat

The flattened, double-layer ribbon of film created when a blown film bubble is collapsed and pulled through nip rollers, measured as a single width dimension.

M

MDPE (Medium-Density Polyethylene)

A polyethylene resin with density between LLDPE and HDPE, offering a balance of stiffness and toughness, commonly used in bags and protective packaging.

Masterbatch

A concentrated pellet form of additives or color pigment carried in a resin base, blended into base resin at a small percentage during extrusion.

Melt Index

A standardized lab measurement of how easily a molten resin flows, expressed in grams per ten minutes, used to predict how a resin will process.

Metallocene LLDPE (mLLDPE)

A premium grade of linear low-density polyethylene made with metallocene catalysts, offering tighter molecular control and improved strength, clarity, and sealing.

Multi-Layer Film

Film made of two or more distinct resin layers bonded together during extrusion, each layer engineered to deliver a specific performance property.

P

PCR Resin (Post-Consumer Recycled Resin)

Plastic resin reclaimed from used consumer packaging or products, cleaned and reprocessed into pellets that can be blended back into new film.

R

Rollstock

Finished film wound into rolls and supplied as raw material for a customer's own packaging, printing, or converting equipment, rather than as finished bags.

S

Seal Strength

The force required to peel or break apart a heat seal joining two layers of film, used to confirm a package will hold together without failing in use.

Shrink Film

Film that has been stretched and oriented during production so it shrinks tightly around a product when heat is applied, commonly used to bundle multipacks.

Slip Agents

Additives blended into film resin that migrate to the surface and reduce friction, helping film slide smoothly through packaging and converting equipment.

Stretch Film

A highly elastic film, usually LLDPE-based, that is stretched around a load at the point of use and relies on elastic recovery to hold the load tightly together.

T

Tensile Strength

The maximum stress a film can withstand while being stretched before it breaks, typically measured separately in the machine and cross directions.

Tie Layer

A thin internal layer in a coextruded film, made from a special adhesive resin, that bonds two otherwise incompatible layers together.