Glossary of packaging terms

Polybags Direct is committed to providing packaging knowledge. The following list is a glossary of terms used in the packaging industry.

Modified atmosphere packaging MAPThe use of gas flush vacuum packaging to change in atmosphere within the package. Packaged salads, nuts, chips and meats are packaged with gas flush.
Bags on a rollContinuous roll of seamless tubing perforated under bottom seal. Bags must be torn off to open.
Bottom seal bagsIndividually cut bags from seamless tubing, sealed on the bottom. Flat or side gusseted bags with a strong seal.
Butylated hydroxytoluene BHTA fat-soluble organic compound that is primarily used as an antioxidant food additive as well as in cosmetics, pharmaceuticals, jet fuels, rubber, petroleum products and embalming fluid.
Biaxially oriented polypropylene BOPPA material used for resealable lip and tape. This material offers an even higher grade of clarity and is resistant to tears and wrinkles.
CaliperThe thickness of sheet material expressed in "points" or mils (thousands of an inch).
Cast filmThe fabrication of a film by continuously pumping the polymer through a straight slot die, then chilling this hot plastic immediately through contacts with a chilled roll. Film width is determined by how fast the chill roll pulls the film away from the die.
Center fold filmA film that has been folded in half,lengthwise.
Center folderA mechanical device used to create center folded film.
ClarityTransparency of the film based upon surface gloss and haze.
Co-extrusionTwo or more polymers extruded and combined in a die, each forming a distinct layer in the final film.
Co-polymerCo-polymer Result of two monomers being combined through polymerization.
CoreA paper tube on which film is wound.
CorrugatedA durable, lightweight material used for making cases. Corrugated packaging has an arched layer, called fluting, between smooth sheets, called liner. The corrugated cardboard most commonly used to make cases has one layer of fluting between two smooth sheets.
CellophaneClear film derived from wood pulp has a memory and will crinkle like paper, it is a thin, flexible, transparent film formed from cellulose fibres. Cellophane is widely used in food packaging due to its high moisture barrier properties and sealability and is biodegradable.
DieA device used in extrusion processes to shape the extrudate.
Dwell timeThe time usually expressed in seconds at a given temperature that is required for the application of heat to seal a heat sealing membrane.
ElasticityThe ability of paper or plastic to rebound back to its original state after being stretched.
ExtensibilityThe ability of paper or plastic to be stretched without breaking.
ExtruderA machine that makes stretch film. It consists of a large steel barrel surrounded by heaters, which melt the plastic resin pellets. Inside of the barrel is a large screw to force the liquid plastic under pressure through a die to be made into plastic sheeting by either the cast or blown processes.
ExtrusionA product formed by pushing material through a die.
Extrusion laminationA laminating process in which individual layers of multi-layer packaging materials are laminated to each other by extruding a thin layer of molten synthetic resin (such as polythene) between the layers.
End (bottom) weldA bag with the seal at the base of the bag. The seal is separated from the end of the bag by a small skirt. Bag length is measured from top to bottom of the bag including the skirt.
Euro-palletA euro-pallet measures 1200mm x 800mm. A euro-pallet is smaller than a UK pallet.
EuroslotA horizontal slot punched in the bag for hanging.
Electrostatic discharge (ESD)Electrostatic discharge is the sudden flow of electricity between two electrically charged objects caused by contact.
EPI Environmental Technologies (EPI)EPI Environmental Technologies has been designed to control and manage the lifetime of products made from plastics.
Flat bagsTwo-dimensional bag (width x length) with bottom or side seals.
FlexibilityThe property of a material, which will permit its being bent or twisted without breaking, the state of being non-rigid.
Four color process printingIndicates the four-color plates or cylinders commonly used in color printing.
FlushA term used in layflat tubing whereby the film is rolled right up to the edge of the core.
Faraday cageA Faraday cage or Faraday shield is an enclosure used to block electromagnetic fields.
GaugeA term used in referring to the thickness. The higher the gauge the thicker the material.
1 mil1/1000 of an inch
1 mil25.4 microns
1 micronOne millionth of a meter
1 inch25.4 mm
100 gauge1 mil
80 gauge8/10 mil
Gauge bandThickness irregularity in films.
GussetGussets are traditionally added to clothing to add breadth. Gussets are also a way of making polythene and paper bags bigger. Paper bags can have a bottom gusset. Poly bags can have a side gusset.
Gusseted bagsFlat style bag with both sides or bottom tucked in to form gussets. Designated with three dimensions; Side Gusset (width x depth x length) or Bottom Gusset (width x length + gusset).
Grip sealA bag which is resealable and reclosable by two plastic components interlock at the top of the bag. The bag is reusable and flexible.
Gusset sealA flat-style bag manufactured with both sides tucked in to form gussets.
Grams per square meter (GSM)Refers to the substance weight of paper, relating to an area of paper that remains constant. Standard printer paper is around 80 GSM.
High density polythene (HDPE)This blend of material offers higher strength material when compared to normally LDPE film. It can be blended with any of the above material to boost their puncture resistance. However the most common use for this blend is on thin gauges as it allows you to down gauge, however still have the same strength as the thicker material. One downside to HDPE film is that the clarity is not as good as LDPE film. Common usages include grocery bags and trash bags.
Hole punchA mechanical device used to produce an air evacuation hole.
Half moon hole punchA punch hole that has not been completely cut through. Air is still able to escape through the bag.
Hot melt adhesiveStick to almost anything: foams, corrugated cardboard, fabrics, plastics light-gauge metals. Hot melts are as strong as mechanical fasteners and sealing tapes. Hot melts are virtually invisible therefore improving overall aesthetic.
Impulse sealerAlso known as a heat sealer. These units use an electrical current passed through a wire heating element to seal the tubing. Impulse heat sealers be used on many plastic materials to create strong permanent welds.
InchA unit of length in the British Imperial system.
KeylineThe guide used in making plates or engraving cylinders and printing a piece - a diagram of copy and art for reproduction.
LaminationComposite product consisting of two or more sheets or films joined together with glue or adhesive.
Low density polythene (LDPE)LDPE film is resistant to punctures and tears, non-porous and stretchable. LDPE has good clarity but weak film strength. Primarily used for plastic food bags and poly sheeting.
Linear low density polythene (LLDPE)LLDPE film has higher tensile strength and higher impact and puncture resistance than the LDPE. Mainly used for stretch film.
LipOne side of the bag is longer than the other, allows bag to be opened more easily.
Medium density polythene (MDPE)Film that has higher stiffness, higher melting point and better water vapor barrier properties. Common usages include gas pipes and heavy duty shrink films.
MemoryThe ability of a film to maintain its characteristics after shrinking.
Metric conversions
1 kilogram (kg)2.2046 pounds
1 meter39.37 inches
1 pound1.0936 yards
1 mill1/1000 of an inch
1 micron1/1000000 of a meter
1 inch25.4 mm
100 gauge1 mill
80 gauge8/10 mill
MillimeterA unit of length. One-thousandth of a meter or a one-tenth of a centimeter.
MillThickness of material. The higher the mill, the stronger the material. 1 mill is 1-thousandth of an inch.
MicronThickness of material. 1 micron is 1-millionth of a meter.
NylonPolyamide resins, with very high melting points, excellent clarity and stiffness. Two types are used for films: nylon-6 and nylon-66. The latter has much higher melt temperature, thus better temperature resistance, but the former is easier to process and it is cheaper. Both have good oxygen and aroma barrier properties, but they are poor barriers to water vapor.
OpacityHiding power of pigmented (mostly white) plastic films. It is beneficial for packing materials sensitive to light (visible or ultraviolet).
OpaqueA coloured film where you can not see sunlight through the film.
Oriented polypropylene (OPP)OPP film has high tensile strength. The film is transparent in colour and can withstand high temperatures. OPP film is food safe and environmentally friendly. It is often used to package confectionery, finished products, spices, vegetables and bakery products. The film can also be used for packaging cosmetic and medical products.
PalletA rigid platform used as a base for transporting goods as a unit load. A standard UK pallet measures approximately 1000mm x 1200mm.
Pallet wrapPallet wrap stretchwrap that is used to bind a pallet together.
PerforationsThe practice of creating a long series of holes so that plastic film can be torn more easily. Postage stamps are one common application of this.
PolytheneA simple thermoplastic polymer of ethylene. Highly puncture and tear resistant. Not affected by extreme temperatures. Does not possess barrier properties. Good clarity. Depending on its density, it may be low density (see LDPE). Medium density (see MDPE). High density (see HDPE).
PolymerA material made through the process of polymerization.
PolyethylenePolyethylene or polythene is the most common plastic. Polyethylene is of low strength, hardness and rigidity. Polyethylene has a high ductility and impact strength as well as low friction. It shows strong creep under persistent force. It feels waxy when touched. Most grades have excellent chemical resistance, meaning they are not attacked by strong acids or strong bases and are resistant to gentle oxidants and reducing agents. Depending on film thickness, polyethylene can vary between almost clear (transparent), milky-opaque (translucent) or opaque.
PolymerizationA gas heated under pressure to form a solid.
PolypropylenePolypropylene film helps to preserves freshness with vapor and moisture barriers. The film is non-porous and has excellent clarity. Polypropylene film can withstand high temperatures.
Poly vinyl chloride (PVC)A tough, stiff, very clear film. The oriented version is used mainly for shrink film applications.
Printed warning notice (PWN)A simple printed warning about the danger of suffocation with polythene bags.
Reclosable bagsSeal-top reclosable bags can be made with or without a tamper-evident adhesive seal. Also includes zipper and slider zipper bags.
RecoveryStretch film trying to return back to its original form after it has been stretched. This action constantly pulls the load together since the stretch film tightly form-fits the load. Stretch wrapping continues to tighten the load as it settles during shipment, due to the recovery property, keeping the load safe and secure during shipment.
Resin identification codeResin identification codes (RIC) are codes defined by the European Commission. They identify the recyling status of a material.
RIC 05 polyproplene#5 PP applies to polypropylene and indicates the material is recyclable.
RIC 04 low density polythene#4 LDPE applies to low-density polyethylene and indicates the material is recyclable.
Seal strengthMeasurement of force required to break or destroy a heat seal formed by any of the heat sealing sheets.
SheetingThe cutting of a large master roll into sheets.
Shrink wrappingA technique of packaging in which the strains in a plastic film are released by raising the temperature of the film, thus causing it to shrink over the package.
Side weldBags that are sealed on the side only. Has no bottom seal.
Singlewound filmA single layer of shrink film wrapped around a core.
SlittingThe cutting of a large master roll into smaller rolls used.
StaticAn electrical charge built-up in plastic film.
SealTerm used to describe the seal at the bottom of a can liner. The three types of seals are flat, gusseted and star.
Shielding bagA bag used to shield the contents from electromagnetic radiation. A metallised bag is a form of shielding bag.
Tear resistanceThe ability of a film to resist the propagation of a tear.
Tensile strengthThe ability of a material to resist a direct pull. Higher tensile strength is generally preferred for packaging products. When packaging heavier products a packing tape with higher tensile strength is preferred to help ensure a better seal. A stretch film with higher tensile strength will reduce shipping damages and increase load stabilization.
ToleranceAllowable deviation from a nominal or specified dimension. Minimum/maximum range of measurement.
Top sheetingA protective covering put on the top of a load to protect the top from dust, dirt and other objects that might damage or dirty the load.
TintFilm where only a little masterbatch is added to give a tint of colour.
Totally degradable plastic additives (TDPA)TDPA is produced by EPI Environmental Technologies. TDPA is designed to manage the lifetime of polythene products. Once their useful shelf life has passed they will degrade and then biodegrade into environmentally friendly products in a matter of years (rather than centuries). This type of packaging is also referred to as 'degradable' or 'oxo-degradable' packaging. Our LDPE polythene film is made from a virgin polymer. We add EPI additive to increase its biodegradability. Essentially EPI's TDPA provides a way to make conventional plastics degradable and biodegradable.
Vent holeAir evacuation holes in a film made by pin perforators.
Zip top pouchA reclosable or resealable pouch produced with a plastic track in which two plastic components interlock to provide a mechanism that allows for reclosability in a flexible package.

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