Category Archives: Polythene News

Recycling – What are we doing for the environment and what can we help you to do?

What are we doing for the environment and what can we help you to do?

STM Packaging Group recycles all of its process and office waste (and always has done!)

Our own process waste polythene, plus material returned from our customers, local companies, and individuals goes to a specialist reprocessor, Chase Plastics, a key partner to our Group. They reprocess the clear and mixed coloured waste separately and return the recycled polymer granules to us. Due to Chase Plastic’s unique double clean process, this material is returned with very low odour levels. We then make new products with those polymer granules – recycled clear bags, grey mailers and tube film for lots of suitable applications.

We also recycle all of our waste boxes and office paper through the usual paper recycling channels. In addition, we donate our broken pallets, waste reel cores, and any other wood waste to members of our staff with multi fuel burners to generate free and carbon neutral heat for their homes.

“But how can polythene be a good option?”

All polythene (LDPE) is recyclable. This is a key question we are being asked by customers and end users alike. To help to explain this, we have advanced plans in place to add a ‘recyclable’ or ‘recycled’ message to all of our stock mailing bags to increase public awareness and to help improve recycling levels of the product from the domestic environment. We can also offer a wide range of recycled films. Please ask one of our expert advisors if this is of interest to you and your customers.

To recycle all of your polythene products, you can return it to STM Packaging for reprocessing. If this is not convenient, you can put all polythene products into the supermarket carrier bag recycling stations and they will recycle them for you.

carrier bag recycling stations

reduce reuse recycle symbolAn exciting new project!

STM Packaging is working on a new project – we are trialling a film made from corn starch which is 100% biodegradable – we will let you know as soon as this product is available!

We believe it is great to see so many new initiatives being developed to address the effects of plastics in the environment. One eye-catching scheme in the media recently was RPC bpi, a leading plastics company, recycling very low grade polythene waste into polymer granules to be used in road building. What a fabulous use of the material where it can never litter or get into the wider environment while saving the natural resources of making bitumen.

If you have any further questions for us on this hot topic, please don’t be shy – ask us, and we are sure we can help to assure you and your supply chain of the credentials of using an ethical polythene company!

How do we print your custom design?

Here at The Polythene Company we print custom designs with artwork ranging from simple text, to highly detailed pictures. We thought we’d give you an insight into just how we make your artwork come to life.

It all starts with you. You send us your desired artwork and we then transform this into a ‘proof’ our plate makers use to design the printing ‘plates’ that we use for making the bags. We can print designs in up to 8 colours using the flexographic print process. Once this has been checked for accuracy and to ensure that there will be no issues with your design, the plates are made.

Just what are ‘printing plates’?

Printing plates are how we transfer the printing ink onto the film that makes the bags. These flexographic plates are made out of a light-sensitive polymer. The design is then created on this plate using UV light to harden the polymer in the design areas.

How do the plates work?

One plate is needed for every colour to be printed. The plates are mounted onto a cylinder which is placed in thea flexographic printing plate printing press. Every colour has to align perfectly with each other to make sure the design is printed properly, or in “register”. After this, the ink is transferred from the ink roll which is flood-coated with ink. It then transfers to the ‘anilox’ roller which holds a specific amount of ink on the surface as it is covered with thousands of small wells that enable it to transfer ink to the printing plate in a uniform thickness evenly and quickly.

How does the ink adhere to the surface of the polymer film and not rub away or crack?

Our film is specially treated using a method called Corona treatment. This treatment involves using a high frequency discharge that increases the adhesion of a plastic surface on one side. This side is the side used for printing on. The ink will then adhere to the polythene film and not rub off, crack or fade.

The printing is then complete!

The film is always printed before conversion, so once the film has been run through our printing machines it is then ready to be taken across to the conversion machines. The conversion machines then turn the film into your polythene bags.

ink, printing plates and customised images

If you want any further information regarding the above, check out our custom mailing bags, or contact one of our friendly team members who will be happy to answer queries.

Daisy printed mailing bags

Our new Daisy divinely different® design is here!

We’ve added another brand new design to our divinely different® printed mailing bags range – Daisy!

We love our divinely different® range so much that we’ve added another brand new design! It comes in four fantastic bold colours to suit any theme. This means you can make an eye-catching impact when sending our your products at a great price.

Polka dot printed mailing bags
Daisy turquoise printed mailing bag
Green daisy printed mailing bag
Pink daisy printed mailing bag
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With this new new design you can expect the same great quality as our other products. Each bag is sure to have the following:

  • A strong, permanent ‘peel and seal’ adhesive flap.
  • Super tough side seams, manufactured using 50micron co-extruded film.
  • Opaque and weatherproof so the contents stay safe and secure.
  • Eye-catching designs in vibrant colours.
  • A blank address area suitable for pen or labels.

Our Daisy printed mailing bags are available in the most popular mailing bag sizes:

  • 162mm x 230mm + 40mm lip for your C5 sized items
  • 250mm x 350mm + 50mm lip for your C4 or slightly oversized C4 items
  • 330mm x 440mm + 50mm lip for C3 sizes items.

Please don’t hesitate to contact our experienced sales team today to discuss products or to place an order for next day delivery.

introducing our new splatter design to the divinely different packaging range

Splatter joins our growing divinely different range®

Our divinely different® range welcomes a brand new design – Splatter!

Here at The Polythene Company we recognise how popular our divinely different® range is with our customers and therefore we’re always on the lookout to add new designs. We’ve created this brand new Splatter pattern – a bold and striking design guaranteed to grab attention.

splatter bags in blue and black

With our new designs you can expect the same great quality we deliver with  our other designs, including all of the following:

  •  A strong, permanent ‘peel and seal’ adhesive flap.
  • Super tough side seams, manufactured using 50micron co-extruded film.
  • Opaque and weatherproof so the contents stay safe and secure.
  • Eye-catching designs in vibrant colours.
  • A blank address area suitable for pen or labels.

Our Splatter mailing bags are available in the most popular mailing bag sizes:

  • 162mm x 230mm + 40mm lip  for you C5 sized items
  • 250mm x 350mm + 50mm lip for your C4 or slightly oversized C4 items
  • 330mm x 440mm + 50mm lip for C3 sizes items.

Please don’t hesitate to contact our experienced sales team today to discuss products or to place an order for next day delivery.

sequential numbering on polythene bags

Sequential numbering on polythene bags

Sequential numbering on polythene bags explained

Sequential numbering on polythene bags can be confusing so that’s why we’ve put together this guide to explain the uses and the various ways this can be customised to suit your needs.

sequential number in a box

What are sequentially numbered bags used for?sequentially numbered polythene cash bag

Sequential numbering is used on polythene bags to specifically identify the bag. The most common sequential numbering is for cash collection as well as returning gift vouchers or coupons.  Other uses include storing personal staff belongings i.e. on planes, trains etc.. Another use can be for holding confidential documents or products, such as exam papers, which need to be officially logged and recorded.


sequentially numbered bagHow many numbers can be printed?

Our conversion machines can print one number with up to 8 digits on any bag. This can also include dates or letters depending on what your business requires.  These numbers or letters can be printed anywhere on the bag provided that enough space is left on the design. Even with an 8 colour print you can still have the bags sequentially numbered. If you need the numbers to line up with a printed security box this is no issue and can be easily implemented. For further information on how you can customise your polythene bags visit our custom mailing bag page.


How does our machine work?sequential numbering machine

The machine we use for sequential numbering sprays the number in ink whilst the bag is being converted. Our machine can produce up to 100 bags per minute using this method. The design is printed first, and then during conversion the number is sprayed onto the bag.


polythene bag with a barcodeCan the bag also have a barcode?

Yes  – the sequentially numbered bags can also accommodate a barcode. If the film is clear a white block will be needed for the barcode to ensure this is able to be read by machines that use them. However, if printing on an opaque polythene film, such as co-extruded or grey, then you can place the barcode and sequential numbers directly onto the film. The numbers can be printed directly onto clear film with no problems but an eye-mark will be required to ensure the numbers stay in the same position on each bag during conversion.



If you have any queries or would like to place an order please get in contact with our friendly team.

Hot pink polka dot printed mailing bag

New hot pink polka dot printed mailing bags

Please give a warm welcome to our new hot pink polka dot colour

Hot pink polka dot printed mailing bagHere at The Polythene Company we wanted to banish the January blues with a brand new hot pink polka dot design in our divinely different ® range. If you have previously purchased our divinely different® star printed mailing bags in “Neon-light” pink you may already recognise the colour, it’s so popular and we loved the colour so much that we couldn’t pass up the opportunity to add it to the polka dot range!

The polka dot range has gone from strength to strength since its creation a couple of years ago. At the beginning we only started with 3 colours (pink, green & blue) and now with the addition of Hot Pink we have grown to a range of 10 popular colours.

Still to this day, we are the only UK manufacture of our divinely different polka dot mailing bags and you can expect the following while using them:

  •  A strong, permanent ‘peel and seal’ adhesive flap.
  • Super tough side seams, manufactured using 50micron co-extruded film.
  • Opaque and weatherproof so the contents stay safe and secure.
  • Eye-catching designs in vibrant colours.
  • A blank address area suitable for pen or labels.

Our Hot Pink polka dot mailing bags are available in the most popular mailing bag sizes:

  • 162mm x 230mm + 40mm lip for you C5 sized items (coming soon)
  • 250mm x 350mm + 40mm lip for your C4 or slightly oversized C4 items (coming soon)
  • 330mm x 440mm + 40mm lip for C3 sizes items.

Please don’t hesitate to contact our experienced sales team today to discuss products or to place an order for next day delivery.

CMYK colours and Pantone logo

CMYK vs. Pantone® in solid colour printing

What is the difference between CMYK and Pantone® (PMS) when using solid colours in flexographic printing?

Here at The Polythene Company we’re experts in polythene and flexographic printing. We print and manufacture on site in our UK factory so we understand all the terms, but we also understand that not all our customers do so we wanted to shed some light on one of the most common queries. When discussing custom printed mailing bags, you may find you’re often asked if the colours for your custom print mailing bags are CMYK (also known as 4 colour process) or Pantone®/ PMS (sometimes referred to as a spot colour). To designers and printers, like ourselves, these terms are common knowledge, but to a business owner who wants to design a bespoke printed mailing bag this question may lead to confusion.

What does CMYK and PMS stand for?

PMS stands for Pantone® Matching System, a standardized colour matching system used primarily in printing but also throughout a variety of industries. CMYK stands for Cyan, Magenta, Yellow and Black; these are the primary colours for print. The confusion usually stems from what we’re taught at school regarding primary colours; yellow and blue make green, yellow and red make orange and so on. However, in the flexographic printing industry the varying the quantities of cyan, magenta, yellow and black are what we use to create an endless array of colours to print.

Why choose a Pantone® colour?

There are many times when CMYK is the only way to produce your image, such as photos and gradient graphics, but we’re just discussing the use of colour for what we refer to as solid colours. There can be so much variation in colour using CMYK for a solid colour that Pantone® set out to create a system that allowed for consistent colour. This way a designer can create a logo that will print consistently from job to job and printer to printer. Pantone® colours are also easy to convert into RGB and Hex colour values, so you can even keep your colour consistent across websites and digital designs etc.

If you’re using PMS then you will be asked for the pantone reference number, at The Polythene Company we deal with the coated Pantone® references only (there are a variety of different Pantone® series for different materials). We use this system ourselves for our own brand colour on our printed polythene mailing bags, as well as across the board on all branded items, meaning we can guarantee consistency throughout our branding and save on cost!

Here is an example using our Polythene Company branded purple which is 2602c:

Purple CMYK colour breakdown
Coated Pantone® Purple 2602 chip     Pantone® chip of our company colour.

To print the above purple we would need to break it down into four different colours which can be expensive, but as it’s a PMS colour we can buy the Pantone ink already mixed. The Pantone® system means we can generate the exact same colour time after time! It also means that it’s made up of one colour component as opposed to potentially four so it will only require one printing plate per solid “spot” colour as it’s done in a single run as opposed to multiple runs to mix the colours. We know that cost is a key factor in all bespoke mailing bag purchases so it’s even better to have a cost-effective choice that guarantees a high quality, and more importantly, reliable finish.

Comparing equivalent colours of CMYK and PMS:

Another question we’re often asked is what happens when you convert a PMS colour to CMYK. This image below shows how much density you lose in converting from a Pantone® colour to CMYK:

Pantone® and CMYK colour comparisonPantone® and CMYK colour comparison

As we print in house on our flexographic printer we work with PMS colours on a regular basis so we know that these colours offer a tonal range that CMYK can’t. You may have dealt with CMYK previously and want to convert the other way, if so this not a problem as we have swatch books that allow us to find the PMS value for any type of CMYK work you have done in the past.

If you have any other questions regarding bespoke printing and custom mailing bags, then please don’t hesitate to contact our experienced sales team who can help you every step of the way!



Polythene reel films

How we manufacture polythene products

We may be experts in manufacturing polythene but we understand that not all of our customers are!

Here at The Polythene Company we’ve found that many of our customers are interested in learning how their products are manufactured. Unfortunately, we can’t take everyone on a tour of our factory so we thought we’d do the next best thing and create a step by step guide explaining how we manufacture your envelopes and mailing bags:

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Step 1 – Loading the polythene filmPolythene reel film

The polythene film, printed or plain, is loaded onto the end of the conversion machine. Typically the weight of the reel being loaded is around 85kg.



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Polythene bags manufacturedStep 2 – Setting the tension

Tension rollers are used to keep the film from becoming slack throughout the manufacturing process. The film runs through a series of these rollers before the next step.



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Step 3 – Folding the filmManufaturing polythene envelopes

The polythene is then fed over a kite which folds the film to the finished height, or depth, of the envelope.



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Polythene bag glue stripStep 4 – Adding the glue

If required, a ‘peel and seal’ glue strip is then added to the flap. Other additions are also made at this stage, such as sequential numbering,  safety hole punches and euro-slots.



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Step 5 – Cutting and sealing the bagManufacturing polythene bags

The polythene film now just needs to be cut and sealed to the specified finished size. This task is carried out by a hot knife which cuts and seals the polythene at the same time. The hot knife normally operates at a temperature of 350 degrees centigrade.



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manufacture polybagsStep 6 – Packing the finished product

Finally your product is made! The finished envelopes or bags are then neatly packed into the appropriately sized box, and if necessary they are then palletised.



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Now your items are ready for a next day delivery!


Clear polythene bags

The widest range of clear polybags

With such a wide choice available how do you know which clear polybags are best for what application?

At The Polythene Company we stock a huge array of clear polythene bags and clear envelopes, all of which feature a peel and seal glue strip. Our clear polybags are manufactured in-house at our Norwich site and with 26 variations available for a next day delivery, you can rely on a speedy service! With all these options we understand that it can all seem quite confusing at first to decide which product best suits your needs, so we’ve created a guide which will hopefully ‘clear’ some up that up for you:

C6 sized bags:
  • Available as either a loose version or block-headed.
  • C6 bags measure 120mm x 160mm (4.75” x 6.3”) and as you would expect will comfortably fit A6 sized items.
  • The loose clear polybag  is manufactured in 50 micron polythene, this thickness of film will hold approximately up to 500g in weight.
  • The block-headed version is manufactured in 35 micron polythene and will hold items up to approximately 250g.
C5 sized mailing bags:
  • C5 clear polybags are available as either loose or blockheaded.
  •  Measuring 162mm x 230mm (6.3” x 9”), they’ve been designed to qualify as a Royal Mail ‘Letter’ size.
  • Please be aware though that items over 5mm in thickness may not qualify as a Royal Mail ‘Letter’ size.
  •  Our C5 clear polybags will hold A5 sized items perfectly, such as brochures and flyers.
  • The loose polybag is available in 35 micron polythene and comes either completely clear or with a white mailing band pre-printed to assist with mailings of brochures or catalogues.
  • Our block-headed version is manufactured in either 30 micron polythene, which will hold up to 200g, or a 50 micron polythene which will hold up to 500g.
  • In addition, there is also a 35 micron oxo-degradable option.
  • Why not try our C5 polypropylene bags? Perfect for when you require a high clarity, classy finish, especially useful for products which require display.
DL sized mailing bags:
  • What does DL stand for? In the envelope world it stands for Dimension Lengthwise, a standard paper envelope size.
  • These loose clear polybags are available in 35 micron polythene measuring 115mm x 230mm (4.5” x 9”).
  • They are very popular as mailing envelopes and a carrier sheet would also negate the need for a mailing label.
B5 sized mailing bags:
  • The B5 size bag, our newest stock item, measures 195mm x 255mm (7.5” x 10”).
  • This polybag is only available as a 35 micron block-headed version.
  • It is perfect for B5 sized catalogue mailing and is proving very popular with mailing houses.
Square sized mailing bags:
  • Our 230mm x 230mm (9” x 9”) square sized clear polybag is an unusual size but one that has proved to be very popular with all manner of businesses.
  • Manufactured in 35 micron polythene, these polybags will hold a wide variety of items up to approximately 250g in weight.
C4 sized mailing bags:
  • By far the most popular size, and as you would expect the one with the most options available.
  • Perfect catalogues, brochures, magazines and promotional items, the C4 size measures 230mm x 305mm (9” x 12”) and easily qualifies as a Royal Mail ‘Large Letter’ size.
  • Three different polythene thicknesses are available in the loose version; 35 micron, 50 micron and a heavy duty 70 micron which will hold up to approximately 1kg in weight.
  • The C4 clear polybags are also available in a loose option with a pre-printed white mailing band.
  • The block-headed polybags are manufactured in both 32 micron and 50 micron.
  • In addition, a block-headed 35 micron oxo-degradable version is also available.
  • Finally, a high clarity finish a polypropylene version is available, manufactured from 50 micron cast polypropylene.
Oversized C4 mailing bags:
  • For those items that are just a little bit too large for a standard C4 polybag, oversized C4 polybags are available.
  • Both the loose and blockheaded versions are manufactured using high quality 50 micron clear polythene.
  • The loose option measures 255mm x 330mm (10” x 13”).
  • The blockheaded option measures 255mm x 355mm (10” x 14”), please note this size will not be suitable for Royal Mail ‘Large Letter’ requirements.
C3 sized mailing bags:
  • Perfect for A3 documents, pads and other flat items, C3 clear polybags measure 310mm x 435mm (12.25” x 17”).
  • These polybags can hold up to 500g in weight as they are manufactured using 50 micron polythene.

Please note:
the depth of your item can affect the size needed (for example a really thick brochure), so even though your item may have the correct dimensions for one of the above sizes you will have to consider a slightly larger bag in order to seal the polybag properly. One of our larger stock bags may be suitable or we can even tailor make a bag to your specification!

As well as our wide range of stock clear polybags we can also make custom mailing bags to suit your requirements, please see our custom mailing bags page for information on all the options available. For further guidance, prices or to place an order please contact our expert sales team and be confident we will find the right bag for you. Remember; nobody knows polythene like The Polythene Company!



divinely different printed polka dot mailing bags

Newest colours of polka dot mailing bags

We are excited to announce the newest colours to our popular divinely different® polka dot range of printed self-seal mailing bags – Royal Blue and Coral!

Polka dot printed mailing bagsAs part of the STM Packaging Group we manufacture our own range of printed bags. They come in a variety of popular  styles, colours and sizes.

Our polka dot mailing bags have received a huge response from customers. We know that you all love using them, packing with them and of course receiving them on the doormat or when the postman knocks.

Due to popular demand we’ve added these new colours to our ever growing range to give you more choice. The polka dot range also includes the following colours – Blue, Green, Pink, Silver, Gold, Red and Purple.

All of our divinely different® mailing bags feature a strong, permanent ‘peel and seal’ adhesive flap. They also have super tough side seams therefore what goes in the bag, stays in the bag!

For more information give our team a call on 01603 409999 or visit our divinely different® mailing bag page.

Don’t be stuck doing the same as everyone else – be divinely different®!