Terms & Definitions
Every profession, job, sport or science has its own unique set of words. Call it slang,
jargon or techno-speak, but even packaging with shrink film has its own list of “key
words.” By using these key words, customers, distributors and manufacturers can
clearly communicate needs and characterize film operations.
Air Evacuation – A hole or series of holes placed in the film to allow the excess air in the bag to escape
Angel Hair – Thin strands of film that appear between the sealed package and the seal mechanism.
Angel hair can be caused by too hot a temperature for polyethylene films or too cold a temperature for
Anti-Fog Film – A film containing a wetting agent which reduces the surface tension on the film to allow
water to wet the surface rather than to form water droplets, which can cause a cloudy appearance.
Ballooning – The lifting action of the film away from the product caused by the pressurizing of the excess
air in the bag and the slight expansion of that air from heat during the shrink process. This phenomenon
keeps the film away from any heat sinks (mainly the product) that could cause erratic or undesirable
Bead Seal – The resultant weld caused by the simultaneous sealing and cutting of two, three or more
pieces of film.
Biaxial Orientation – A film that has been stretched under certain temperature conditions equally in both
the machine and transverse directions.
Blocking – A condition where layers of flat film cannot be separated.
Blown Film – Film produced by extruding resin into a tube that is expanded by air pressure.
Bubble – The inflated tube of film in the blown film extrusion process.
Burn Through – A weakening of the film where the heat of the tunnel exceeded the heat resistance of
the film. Typically, it will appear as a hole or a very cloudy area.
Centerfold – A device used to produce centerfolded film from flat film.
Centerfolded Film – Film folded in half which is a function of surface gloss and internal haze.
Clarity – The transparency of the film which is a function of surface gloss and internal haze.
Coefficient of Friction (COF) – A comparative value indicating the ability of the film surface to move
against itself or another surface. The higher the coefficient of friction, the more difficult to slip or move
(tackier). The lower the coefficient of friction, the easier to slip or move (slipperier). COF can be targeted
at two points in the packaging process:
- Cold Slip – This is a measure of the COF when the film is “cold” or at room temperature. Cold
slip is the COF the film inherently has on the roll, through the sealer, prior to the tunnel.
- Hot Slip – This is a measure of the COF when the film is “hot” or immediately exiting the
tunnel. The hot slip of the film will tend to be tackier than the cold slip.
Coextrusion – Two or more different materials simultaneously extruded into a composite film.
Copolymer – A resin polymerized from two or more monomers.
Core – A paper tube used as a base for forming a roll of film.
Cross-Linked – Film that has been irradiated to bond one polymer chain to another, providing consistent
sealing and shrink at a broader range of temperatures; plus greater strength with less burn-through.
Crow’s Feet – The residual wrinkles that can be left in a poorly shrunk package. They are normally
associated with the excess film on the corners of the pouch.
Dancer Bar – A mechanical device used to control the tension of the film between the film unwind and
the film sealing area.
Density – Weight per unit volume. Films with a low density offer more coverage per weight of film.
Dog-Ears – The excessive film extending away from the corners of the pouch formed by placing a threedimensional
item in a flat pouch. Excessive “dog-ears” normally indicates poor shrink technique.
Efficiency Pack – Rolls of film placed on skids without boxes and held in place with plastic cores and
Electronic Hole Burner – A device that uses an electrical spark to burn a hole in the film for air
evacuation during shrinkage.
Electrostatic Seal – An electrostatic discharge is applied to the overlap of two ends of the film. This
keeps the edges aligned until the film blocks together in the shrink tunnel.
Elmendorf Tear Resistance – A measure of the resistance to tear after the film has been cut.
Elongation – The percentage a film will deform or stretch prior to breaking.
Extrusion – A technique for producing film by melting a resin and forcing it through a die.
Fin Seal – A seal formed when heated wheels thermally tack together two layers of film and the excess is
folded underneath the product. Similar to a candy wrapper.
Fin Trim Seal – A seal formed when two layers of film are thermally sealed and the excess trim is cut and
then removed as scrap either by vacuum or a scrap winder. The result is a clean bead seal on the bottom
of the package.
Fish Eyes – The circular or oval patterns that remain on a package which has been poorly shrunk. They
are normally associated with the absence of adequate heat or air velocity.
Fogging – A buildup of water droplets on the surface of a film.
Forming Head (Plow) – A mechanical device used to shape flat wound film into the desired bag shape
needed for a particular package.
Gas Transmission Rate (GTR) – A measure of the rate a gas will permeate through a film.
Gauge – The average thickness of a film.
Gloss – A measure of the reflected light from the film surface.
Haze – A measure of the cloudiness of the film.
Hole Burner – A device that uses a hot wire formed in a circular shape to burn a hole in the film for air
evacuation during shrinkage.
Hole Punch – A device to punch a hole in the film for air evacuation during shrinkage.
Impact Resistance – The resistance to impact of a film based on Spencer Impact testing methods.
Impulse Seal – A seal produced by an intermittent electric pulse which heats a round wire or ribbon to
cut and seal film.
Inverting Head – A mechanical device used to separate and invert centerfold film 90° as the film is
transferred into the sealing device of the wrapper.
Irradiation – A process that uses high-energy electrons to cross-link a film.
Lap Seal – A seal produced by overlapping film and then binding it together either thermally or
Low Temperature Flexibility – The lowest temperatures at which a film can withstand a flexing test
L-Sealer – The most common means of sealing film for heat-shrinkable applications. An L-shape sealer
produces two seals simultaneously on folded film.
Machine Direction (MD) – The direction the film was manufactured and also comes off the roll.
Matting – Condition where two layers of folded film cannot be separated.
Mill Roll – The large roll produced directly off the extrusion lines. This roll will be charted and divided into
many custom rolls.
Modulus – A measure of film stiffness.
Moisture Vapor Transmission Rate (MVTR) – The rate moisture vapor will pass through the film.
Monomer – A simple compound which can react at high temperature and pressure to form a polymer.
Orientation – The stretching technique used to obtain molecular alignment in a film during manufacture,
which increases tensile strength and stiffness and decreases tear strength.
Oxygen Transmission Rate (OTR) – A measure of the permeability of a packaging film to oxygen.
Pinholes – Small holes formed in the seal by tension on the film during sealing or wrinkles in the seal
area. Pinholes can make it difficult to get consistent shrink performance since it affects air evacuation.
Plasticizer – A substance blended into plastics such as PVC to improve flexibility and softness.
Polyethylene – A resin made from ethylene gas that produces tough transparent film.
Polymer – A high-molecular-weight, long-chain compound formed from one or more simple molecules.
Polyolefin Film – Polyolefin is the largest class of thermoplastic films. These films feature very high
resistance to tear and wear and, at the same time, are soft, glossy and flexible. Because of their softness
and flexibility, polyolefin films never get brittle. Clysar
® films fall into the polyolefin family.
Polypropylene – A resin made from propylene gas which produces lightweight, highly transparent, stiff
Polyvinyl Chloride (PVC) – A resin produced from vinyl chloride. It is generally compounded with
plasticizers and other additives to improve flexibility.
Sealing Wire – A nichrome wire that is heated by its resistance to electrical current. It is used for sealing
and cutting shrink film.
Shrinkage/Percent Shrink – The decrease in dimension of a film when it is subjected to heat.
Shrink Film – A plastic film that has been produced under special orientation conditions that allow the
film to shrink when heat is applied. Available shrinkage is usually 50% or greater.
Shrink Force – The force exerted on the product by the film during the shrink process.
Single Wound Film – Flat film wound on a core.
Slip Agents – Lubricants added to films to improve slip and reduce friction.
Static – An electric charge generated by film moving across itself (unwinding from the roll) or any other
Suspend Pack – A method of packaging rolls with particleboard end caps and no boxes. This is usually
used for double-length rolls for added protection because of the heavier weights. Rolls are stacked on top
of each other and then placed on skids and stretch wrapped.
Tear Strength – The ability of the film to resist tearing. Highly oriented films generally have reduced tear
Tensile Strength – The force required to break a film.
Tension – A force exerted on the film from external sources.
Tracking – The ability of a roll of film to be unwound and transferred to the seal area in a smooth and
Transverse Direction (TD) – The direction at right angles to the film movement during its manufacture. It
is usually the same as the width of the film.
Trim – The edges of film which are cut from a package formed on an L-sealer or side sealer when the
seal is made.
Uniaxially Orientated Film (Preferential Shrink Film) – A film that will shrink in only one direction.
Wrinkles – Loose, unshrunk film found along the edges of the package caused by incorrect bag size or
improper air evacuation.
Yield – Coverage of a film per unit weight (usually sq in/lb) rolls.