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We have collated a list of FAQ's that our envelope experts are frequently asked and compiled the into this handy list, providing you with all the important information about our envelopes! Can't find an answer?

Contact one of our envelope experts on (0)1935 477 555

What size is a C5 envelope?

A C5 envelope is 162x229mm (6.4 inches x 9 inches). The most common envelope size you mady find in the post, a C5 will fit A4 paper folded in half. Visit our Envelope Sizes page for more information.

What size is a C6 envelope?

A C6 envelope is 114x162mm and can fit A4 paper folded into four or A5 paper folded in half once. This is a great envelope for sending invitations. Our Envelope Sizes page has further information.

What size is a C4 envelope?

C4 envelopes are designed for A4 size paper, measuring at 229x324mm, it is perfect for sending documents, brochures and marketing literature. You can find a size guide on our Envelope Sizes page.

What size is a DL envelope?

A DL measures 110x220mm and can fit an A4 piece of paper folded into 3 parts, this makes them the perfect envelope for sending compliment slips. The D is short for DIN (deutsche industries norm) and L is for Langer (German for long), together meaning standard long or standard size.

Why do oversized envelopes such as DL+ and C5+ exist?

Oversized envelopes exist to provide an extra bit of space in an envelope for inserting at high speeds. Quite often a mailing may consist of more than one item, and it helps to have extra room so the envelope doesn’t tear. They also run better on mailing machines as they insert better, meaning less stoppages.

How do I know the best envelope for my paper size?

The simplest way to find out if your paper will fit into an envelope is to change the ‘A’ for ‘C’. For example an A4 piece of paper will fit into a C4 envelope or A5 into a C5.

How do I know the weight of paper used for my envelope?

If you look for the GSM / Grammage this determines the weight of the paper, measured grams/m2. A larger grammage signifies a thicker paper.

How do I measure the window on an envelope?

You should always measure the distance from the left hand side first and then up from the base of the envelope, ensuring that the flap is at the top. Our Window and Interior Opaques page has more useful information.

What is the difference between a pocket, wallet and a banker envelope?

A Pocket envelope opens on the short side of the envelope whereas the Wallet and Banker envelopes open along the longer side. The Banker has a distinctive ‘V’ shaped flap while the wallet has a shorter squarer flap. For more definitions visit the Glossary of Terms page.

What is a board back envelope?

Board Back envelope is made with a board back & paper front. These are mostly used for sending items that you want to protect from bending for example certificates.

What is a card envelope?

A card envelope is an envelope made completely from card, for instance our Premium Optima range. Sometimes this will refer to an envelope that would be used to send a greetings card in, such as our invitation envelopes.

What is a gusset envelope?

A gusset envelope is a pocket envelope with expandable sides. These can have either, a block bottom or V- bottom. All our gusset envelopes are V-bottom so they are suitable for over printing.

What is a BRE envelope?

A BRE or Business Reply Envelopes are often enclosed with direct mail as a means to reply directly to sender without the recipient incurring any postage. BRE's tend to be undersize DL & C5. For more information take a look at our Glossary of Terms.

Which envelopes are best for invitations?

The best envelopes to use for invitations are a gummed envelope with a diamond flap, sometimes these are referred to as a 'Banker' or a ‘Diamond Flap’.

What is the difference between inside and outside side seams?

Inside seams are glued inside the envelope and outside seams are on the outside. Mailing houses usually prefer outside seams as they don’t catch on mailing machines, whilst printers may prefer inside seams for printing on the envelope reverse. It’s all down to preference!

How much more expensive is paper based packaging than plastic packaging?

Paper costs approximately two and a half times as much as polythene by weight.

How much more will I have to pay for a Kraft mailing bag compared to the polythene mailers I currently use?

Paper mailing bags cost approximately two and a half times more than their plastic equivalent.

What is 'Plastic Tax' and what are the implications?

This is a new tax that will apply to plastic packaging manufactured in, or imported into the UK, that does not contain at least 30% recycled plastic. Plastic packaging is packaging that is predominantly plastic by weight. It will not apply to any plastic packaging which contains at least 30% recycled plastic, or any packaging which is not predominantly plastic by weight. Imported plastic packaging will be liable to the tax, whether the packaging is unfilled or filled. For more information, visit:

How waterproof are Kraft mailing bags against polythene mailers?

Most water leakage on any mailing bag comes in and around the flap & seal, therefore if it is only light or medium exposure to moisture, Kraft mailing bags will keep the product protected in the same way as polythene. If it is heavy or prolonged exposure to moisture, polythene is an impermeable material and would therefore outperform paper. See our Kraft Mailing Bag video here:


What is Gummed Sealing?

A Gummed Seal is the sealing method that requires moistening to seal. Take a look at our Sealing Methods page for more insight on all our seals..

What is Peel & Seal?

Peel & Seal sealing has a release tape which is peeled away from the envelope flap to reveal a strip of latex which, when pressed down, forms an instant bond. Take a look at our Sealing Methods page for more insight on all our seals.

What is a double Peel & Seal strip used for?

A double Peel & Seal strip is especially common in ecommerce packaging products. This allows the packaging to be reused again using the second seal e.g. for returns.

What is Self Seal?

A Self Seal envelope has the sealing method where two latex flaps are pressed together to form an instant bond. Take a look at our Sealing Methods page for more insight on all our seals.

Are the flaps on a Self Seal envelope open or closed?

They are open. If they were closed they would stick shut!

Do Self Seal wallet envelopes have inside or outside seams?

They are always inside, because if they were outside you would be unable to lift the lower flap to seal the envelope.


Do Blake offer personalisation advice and design services?

Yes, our team work closely with you to create the perfect solution for your needs, utilising the best materials and techniques. If you are in need of more suggestions, guidance and support, we are happy to work with you on developing the idea from the start!

Can Blake provide bespoke sized envelopes?

Yes, beyond our standard stock envelopes, we can create envelopes to any size you may require! This includes external size and shape as well as unusual window sizes and apertures.

Can Blake provide bespoke packaging solutions?

Yes, we regularly produce a vast array of bespoke packaging solutions for both display and mailing purposes. As with our bespoke envelopes, the options are truly infinite.

Which materials can Blake utilise?

Our team can utilise a range of different paper substrates and weights; extra lightweight or heavy bond, colours, textures, beautiful smooth bond papers or papers that are completely handmade. We can even use more diverse materials such as specialist foils, polythene and boards.

Which stock products can Blake overprint?

Alongside creating unique products from conception we also offer a range of Overprint Services to add extra personalisation and impact to your envelopes. We can print on a variety of different stock lines including gussets, board backs, all boards and bubble bags across a range of sizes.

Which envelopes are best for digital printing?

Our Premium ranges are all compatible for digital printing. It is the laser window film that makes this suitable. You can also print on our Creative Colour envelopes for an effective finish to your mailings. Remember digital printing will also allow you to utilise variable data for individual personalisation.

Which envelopes can be put through a mailing machine?

A mailing wallet with a trapezium flap is generally what is required for putting through a mail inserting machine, this is due to the fact they have been designed to work in any mailing machine, making it the best choice for bulk and fast mailings. Mailing envelopes are always gummed as the mailing machine will moisten and seal the closure as part of the mailing process. With both digital and inkjet options available we have the perfect mailing all-rounder!


Which certifications to Blake hold?

Blake are ISO9001, ISO14001 and ISO27001 accredited, and FSC and PEFC chain of custody certified. To find out more, visit our ISOs & Accreditations page.

What are Blake doing to reduce their waste?

We have a goal to reduce our impact on landfill to zero by the end of 2021, and we have a strict recycling scheme in place to promote the recovery of valuable resources. Find out more in our Sustainability & The Environment section.

What does FSC stand for?

This stands for Forestry Stewardship Council and it means there is full traceability on the raw material's journey from forest to doorstep. Discover more in our ISOs & Accreditations section.

What does PEFC stand for?

This stands for the Programme for the Endorsement of Forest Certification, which provides chain of custody certification for all paper based products. Discover more in our ISOs & Accreditations section.

What are the nationally recognized recycling symbols?

Discover these in our How To Recycle section!

What are the United Nations Sustainable Development goals?

There are 17 goals, and we are proud to say we contribute directly or indirectly to them all. They are as follows:

1. No poverty


2. Zero hunger


3. Good health and well-being


4. Quality education


5. Gender equality


6. Clean water and sanitation


7. Affordable and clean energy


8. Decent work and economic growth


9. Industry, innovation and infrastructure


10. Reduced inequalities


11. Sustainable cities and communities


12. Responsible consumption and production


13. Climate action


14. Life below water


15. Life on land


16. People, justice and strong institutions


17. Partnerships for the goals


Why should I buy a recycled envelope?

Buying a recycled envelope means the paper that it is made from is created from pulp that has already been used as paper previously. This means that you are reducing waste and contributing towards the recycling of valued resources.

Are Blake manilla envelopes made from recycled paper?

Yes, all our manilla envelopes have a minimum of 80% recycled content.

Can you recycle window envelopes?

Some window envelopes have biodegradable film which can be recycled, such as our Purely Environmental envelopes. Explore the range here.


How do Blake measure the impact of the Blake Foundation?

Each SchoolBag we donate has an individual tracking number, so we can keep record of how many bags we have donated and, best of all, find out who the recipients are!

How many children have benefitted from the Blake Foundation?

Blake have impacted the lives of over 5,000 children through our many different projects. Visit our Impact page for more information.

Where have The Blake Foundation had an impact worldwide?

To date, we have helped to further the education of children in Zambia, Romania, England, Nepal and The Gambia, and we are always on the lookout for new areas that need our help!

What is inside a SchoolBag?

Each bag we donate is filled with stationery, learning resources and eating utensils that will enable a child to write, draw, colour, calculate, express themselves and above all, learn. Typically, this consists of:

• 10 pencils

• 10 biro pens

• 12 colouring pencils

• Math set

• Ruler

• Pencil case

• 3 exercise books (lined, square and plain)

• Water bottle

• Lunch box and spork


How long does delivery take?

We offer a next day delivery service to any part of the country for orders received before 3pm (this is subject to volume of orders and transport available). Please check with our sales team on all orders placed after 3pm for next day delivery availability and where possible we will oblige.