Glossary 2017-09-22T11:54:30+01:00


Anti-block is an additive which is added to the polymer granule during the extrusion process. The reason it is added is to prevent the film from sticking together and becoming ‘blocked’. Anti-block is normally added by the polymer manufacturers, however it can be added as the polymer enters the machine.

Anti-static is an additive that is added to the polymer granule during the extrusion process. The additive reduces the static electricity with the finished goods. The static is caused by the friction generated while manufacturing the film and it is normally worse in thinner material.

Barrier Film
A term to describe film that is a good barrier to gases, aromas and flavours – typically, high barrier materials are going to be oxygen barrier materials, of which the most common are EVOH and nylon resins used in conjunction with polyethylene. To create the specific barrier required either coextrusion, lamination or coating is used.

This is a material that breaks down and degrades through microbial action. This usually occurs when the material is in the earth or within a landfill site. An additive can be added to the material with aids and accelerates the process.

This is a process of manufacturing polythene bags. The bags are typically in stacks of 50 or 100 with a header strip across the top of the bags, which is separated with a perforation to aid tearing the bags off one at a time. Within the header strip there is normally two punched out holes, enabling the bags to be hung on hooks to speed packing.

An issue that occurs when 2 layer of the polythene become stuck together making it very difficult to open and in some extreme circumstances impossible to open the film or bag. This most commonly occurs with LDPE and LLDPE.

Blow Ratio:
A typical blow ratio is 3:1. This ratio refers to the ratio of the diameter of the bubble blown compared to the diameter of the extruder die. The greater the ratio, generally the stronger the material due to the fact of the stretching and intertwining of the polymer chains.

Bottom Weld:
A bag that has the seal across the bottom of the bag with a same skirt below the seal that continues to the end of the bag with the opening at the top. The bag is measured from the bottom of the bag (including the skirt) to the top of the bag (the opening).

Centre Fold Sheeting (CFS):
This is a format of polythene which is same as ‘lay flat tubing’ however it has a slit down one side. For example 1m wide film would open out to 2m.

Co-extrusion (Coex):
Coex is a process of extruding polythene film. Coex material is made up from a minimum of 2 layers and can have up to 13 layers of different components making up a polythene film. There are many benefits to coex material which include increased strength, opacity, puncture resistance and tear resistance. The most common use for Co-extruded material is for mailing bags as you are able to have a black inside (to increase opacity) and any colour on the outside.

This is a material that is fully degradable in the specific conditions within a compost heap. It requires the presence of certain defined chemicals and/or microbes.

Corona Discharge Treatment:
Corona treating is when film is passed through a device while it is being extruded. The device changes the surface resistivity of the film (effective scuffing the film electronically) which then enables ink and adhesive to bond to the film better and quicker.

Double Wound Sheeting (DWS):
Double Wound Sheeting is made using the same process of ‘lay flat tubing’ however there is a knife inserted either side of the tube creating a double layer of polythene sheeting being wound onto the core.

Die Line:
A line/seam of weakness in the film caused by a small piece of contamination stuck in the die. The die line can be difficult to see, however the film will tear and break easily along this line.

Fixed blades slit the edges of ‘single wound’ and/or ‘double wound sheeting’ so the width of the film can be manufacture within 2mm of the specification. This is more expensive then edge slit due to the fact you are producing excess waste.

Electro-conductive Polymer:
A type of polymer that has a high content of carbon, which helps the dissipation of static electric. The carbon means that it is a black polymer however it is extruded in the same way as LDPE.

A series of indentations in the films to give a cosmetic effect and to aid stacking bags.

A pallet that measures 800mm x 1200mm and some customer insist on having euro pallets as they fit inside racking better. These pallets are smaller than the traditional pallets. We stock both standard and euro pallets.

A hole that is punched into the bags which is then used for hanging the bags on racking.

An additive added to the film which improve the puncture resistance, sealabilty and surface strength.

Flexographic Printing:
A printing process in which ink is coated onto a print plate (usually rubber or plastic) which is then rolled on the film to transfer the ink from the plate to the film to produce the desired image.

Used to describe the profile of a roll of polythene. This refers to either the film is in line with the core i.e. no overhang.

Flame Retardant:
An additive which is added to the film to reduce the flammability of the material.

A unit of measurement used to refer to the thickness of the material. This is the imperial equivalent of micron, 1/1000th of an inch, thus 1 micron = 4 gauge (approx.).

Gravure Print:
A printing process in which ink is smeared onto an engraved metal roller which is then rolled on the film transferring the image. This is a more expensive print process compared to flexographic printing, however give a higher quality finish.

A fold that is formed either side of the film or across the bottom of the bag which causes the closed width to be smaller than the open width. A side gusset is manufacture on the extrusion machines, were as a bottom gusset is produced on the bag machine.

Gusseted Layflat Tubing (GLFT):
Similar to ‘lay flat tubing’ however some of the material has been folded in.

High Slip:
An additive which is added to the film which makes the film more slippery. This can be desired for some applications but can be a hindrance for other applications.

J Fold Sheeting (JFS):
Similar to ‘centre fold sheeting’ however one of the layers is slit down to form a lip on the material. Mainly used for making side weld bags with a lip, i.e. mailing bags.

When two separate films are joined together through the use of an adhesive to combine the best physical properties of both films.

Layflat Tubing (LFT):
A blown tube of material which is made on an extruder, which is squashed down and wound onto a core.

Linear (LLDPE):
A polymer similar to low density polymer (LDPE).

Light Proof:
This is another phrase for opacity, i.e. no light should pass through the material. The phrase light proof emphasises that the film must be opaque as it is likely to be used in a film processing room.

Low Slip:
Used to describe material that isn’t slippery and has probably been made from a polymer that hasn’t had the slip additive packaging mixed with it. Low slip material is used for large sacks that are going to be stacked to prevent them from sliding on each other.

A polythene product that has extremely high clarity and strength, however it is very difficult to extrude and process.

An additive which is added to the polymer to colour the material. Depending on whether a tint or opaque colour is need, the percentage of masterbatch can range from 1% up to 8%.

A unit of measurement used to refer to the thickness of the material. This is the metric equivalent of gauge, 1/1000th of 1mm (0.001mm).

Tiny holes which are punched within the film making it pervious to air and other gases.

This is a process of extruding a single layer of polythene film as opposed to ‘coex’ material. This type of film is the most commonly used material and it is used to manufacture clear films, polythene bags and some dark coloured mailers i.e. grey and black. Extruding a light colour, i.e. white and yellow are always going to be see through despite the tint. The polythene tube listed on our website is all mono layer film.

This is film that sunlight can’t be seen through. The best way of achieving this is to use coex material as the ‘middle layer’ can be black, which is an excellent “blackout”.

Pallet Wrap:
Pallet wrap a product that is used to bind and secure the contents on a pallet together, the same as stretch wrap. However, they normally come in large rolls, which are usually are used on a pallet wrapping machine.

This is a material which will degrade when left in sunlight. All type of polythene films and bags will eventually degrade in this way, but the photo-degradable additives considerably accelerate this process.

Printed Warning Notice (PWN):
A suffocation warning notice that is printed onto the film or bags to warn against the dangers of the material. The warning is usually printed with black or red ink.

Random Repeat Print:
This is where the print on the material can’t be in register and so the print won’t appear in the same position on each bag during conversion. The repeat length depends on the circumference of the print cylinder and the number of print plates or the number of impressions on the printing plate in use.

Regran (Recycled Material):
Short for re-granulated. Refers to when scrap or excess material is recycled and turned back into a granule. This granule is used to manufacture material therefore giving you a recycled product and a lower quality material compared to virgin.

Registered Repeat:
This is where the print is kept in register to enable the print to be kept in the same position on each bag. The print is kept in register due to the printer using a range of different sized rollers i.e 305mm roller gives you a 305mm repeat. To keep the print in registration on each bag during conversion a registration mark is printed and the mark is then picked up by a ‘magic eye’ (photoelectric cell) on the bag maker.

A processed plastic which has not been used (e.g. factory waste) and subsequently reworked.

Sack grade:
A term to describe a type of polymer, which has a different melt flow index and is suitable to make heavy duty sacks.

Self Seal:
Self Seals are also referred to as Grip Seals are side weld bags with a ridge of plastic profile gripper near the top that clicks together to seal the bag. This seal can be clicked open or shut over and over again. Self seal bags are primarily made abroad and imported.

Shielding Bag:
A specific bag to shield the contents from electromagnetic radiation. A metallised bag is a form of shielding bag.

Shrink film:
This is a film that has been made with a shrinking capability. The film shrinks under the application of heat (e.g. a heat gun or tunnel). Useful for securely wrapping goods onto a pallet and can also be used to prevent tampering of goods.

Side Weld:
A bag that is made from a rube of polythene and is heat sealed and cut on either side of the bags. It is weaker than an end weld bag but cheaper to produce and has no skirt. It it possible to make a side weld bag with a skirt either side – these bags are known as skirt side weld bags.

Single Wound Sheeting (SWS):
A single layer of film wound on to a reel. It is manufactured the same way ‘layflat tubing’ is however the film has a knife inserted on either side of the tube and is then split and wound on two different reels.

A bag that is open both ends rather than sealed at one. In order to produce sleeves the heat sealer is deactivated on the end weld bag maker leaving just the cutting mechanism.

Standard Pallet:
A standard pallet is slightly larger than a ‘euro pallet’ as these pallets measure approximately 1000mm x 14000mm although some pallets variation in size slightly. Recently these pallets have become less frequently used as some companies have standardised racking to take euro pallets.

Stretch Wrap:
A material that is usually PVC or polyolefin based which has plasticising agents added. This is designed to be flexible and stretch around any size or shape product.

Tensile Strength:
Reflates to the maximum load the film is capable of supporting.

This refers to adding a small percentage of masterbatch, changing the colour of the material slightly to the desired colour, however the film is still translucent.

Mailing Bags:
A bag which has had an adhesive strip attached to the top of the bag (usually on a lip). The strip consists of adhesive coated on a non-stick silicone tape which is removed to allow the bag to seal. Depending on the adhesive properties, permanent or resealable bags can be produced.

Please see corona discharge treatment above.

UV Stabiliser:
An additive which is added to the polymer granule. The additive reduces the chances of polythene materials photo-degrade as a result of ultraviolet rays (i.e. sunlight).

Virgin Material:
A term used to describe polymer direct from the manufacturer rather than reprocessed material. As such, we can guarantee it is non-contaminated and can be used for food grade applications.

Water Soluble Bag:
A bag that dissolves after contact with water – useful in certain hygiene disposal applications. The polymer is formulated with alcohol to create the breakdown of the material on contact with the water. The bag can either be soluble in cold or hot water.

Wicketted Bags:
Bags that have been bundled together by means of a small metal hanger or plastic grommets that is put through 2 punched holes near the top of the bag – often used in retail applications or on-line packing machines for easy handling of the bags i.e. bread bags.