All Collections
Mailer Box (FAQs)
Mailer Box (FAQs)

Custom boxes made to ship products of all kinds.

Updated over a week ago


Internal dimensions are useful for working out what will fit inside your mailer box. We recommend adding a 2mm margin on either side of your product to find the correct internal size.

Custom sizing

Custom sizing allows you to create the right-sized packaging for your product. Right-sized packaging minimises the empty space around your product whilst not comprising its safety or your branding. This drives costs down, eliminates waste and reduces your carbon footprint. Right-sized packaging also creates a less frustrating customer experience.

All features, such as a double peel & seal, are available with custom sizes and the same MOQs apply.

Royal Mail Large Letter

Large letter packaging is ideal for items like documents, marketing materials, books and accessories. If you want your mailer box to meet this format, we recommend an internal height of 18mm. This allows for tolerance in board thickness and ensures your box will be within Royal Mail's maximum thickness.

  • Max weight: 750g

  • Max length: 350mm external (330mm internal)

  • Max width: 250mm external (240mm internal)

  • Max thickness: 25mm external (18mm internal)

Royal Mail Small Parcel

Small parcel packaging is ideal for items like clothing, shoes and electronics. This is the most common packaging size for e-commerce businesses.

  • Max weight: 2kg

  • Max length: 450mm external (440mm internal)

  • Max width: 350mm external (340mm internal)

  • Max thickness: 160mm external (150mm internal)


Brown kraft

Brown kraft is one of the most common materials used for mailer boxes. It's cost-effective, and because it's unbleached and uncoated, it's more sustainable than white kraft. As this kraft is brown, colours do appear less vibrant than on white materials.

With brown kraft, all printed sides will be made with slightly thicker paper than unprinted sides. Printed sides will also have a higher percentage of virgin material. This creates the best surface for printing on. The thinner, unprinted sides use less material, which helps keep your mailer box as cost-effective and sustainable as possible.

Uncoated white kraft

Uncoated white kraft is a bleached kraft paper without a coating. This creates a natural, textured feel with no shine. It allows for high-quality printing, but for the best print performance, we’d recommend a premium mailer box that comes with coated white kraft.

Coated white kraft

Coated white kraft is a bleached kraft paper that’s coated in refined clay. This creates a smooth surface for printing. As a result, designs appear crisper than on uncoated kraft paper. Coated white kraft is the best choice if high-definition printing and vibrant colours are important. Coated white kraft will have a slight shine.

If you select a white kraft material but don't print on it, your mailer box will be made using uncoated white kraft. This is brown kraft that's been bleached. It's more cost-effective and more sustainable than coated white kraft and is less prone to scratches.


If you don't select a peel & seal, you will need either tape or a sticker to seal your mailer box.

Single peal & seal

A single peel & seal is a self-adhesive strip that allows you to easily seal a package without tape. All you have to do is peel the backing paper off and seal the flap. Customers can then open the packaging with a tear strip. Choosing a single peel & seal makes fulfilment and unboxing both fast and simple. You can add a single peel & seal to any size mailer box.

Double peel & seal

Instead of one self-adhesive strip, a double peel & seal has two. Which means if a customer needs to return a product, they have a simple, secure way to seal the original package. If they don't return the product, customers will have to remove the second peel & seal before recycling. A double peel & seal includes a tear strip, and you can add a double peel & seal to any size mailer box.

Print colours

A protective coating will be applied to any printed side. This helps protect colours and your design from damage. The coating doesn't affect the appearance, texture or recyclability of the mailer box. Any unprinted side will be uncoated.

Pantone and CMYK

For 1 and 2 colour designs, all colours will be converted to the nearest Pantone colour. This will only affect your design if it’s made of CMYK colours. If your colours need to be converted, we’ll always return your design after to review.

Full colour designs always use the CMYK colour palette. If you want to use both Pantone and CMYK colours in your design, please contact us.

UV varnish

Ultraviolet varnish (UV varnish) is a glossy, liquid coating used to highlight features on printed paper or create a high gloss, professional finish over an entire print area. UV varnish also protects colours from dirt and scratches, and reduces the risk of colours running when wet.

Why choose it?

  • Spot UV varnish can highlight important design elements such as logos and text.

  • A full UV varnish coating can create a high gloss, professional finish over an entire print area.

  • Helps protect colours from dirt and scratches.

  • Reduces the risk of colours running when wet.

Whilst adding a UV varnish has a low impact on your carbon footprint, we recommend using it only when necessary. For example, accentuating a design feature or protecting colours. We don’t recommend adding a UV varnish without a clear purpose. This helps to minimise the impact on the environment.


UV varnish is widely recycled and does not affect the recyclability of paper-based products. This means if your paper packaging has a UV varnish coating, you can dispose of it as instructed.

FSC label

An FSC label indicates the forest-based materials in a product are certified by the Forest Stewardship Council (FSC), a global, non-profit organisation dedicated to promoting responsible forestry.

Whilst there are three FSC labels, all of Sourceful’s FSC certified products are FSC Mix. This means the forest-based materials are from FSC certified forests, recycled paper and controlled wood. If you add the FSC Mix label, the correct files will be included with your dieline and artwork guidelines. You can download these later.

We always recommend including an FSC label so customers know your packaging is certified. If you don’t add an FSC label, your product will still be made with FSC certified materials but there won’t be a label on your packaging to tell customers. You can still market these materials as “from responsible sources”. Learn more



Your order will be shipped by road freight or air freight. Express delivery is the fastest option, making it the best choice for urgent needs, but is much more expensive and less sustainable than Economy.


Your order will be shipped by sea freight. This is the most cost-effective and the most sustainable option but lead times can be significantly longer than Express. We always recommend sea freight unless you need an order urgently.


Split delivery allows you to split a single order and send it via both air freight and sea freight. This means you can benefit from air freight’s shorter lead times whilst balancing costs and your carbon footprint. With split delivery, you can choose how many units you want to send by air freight versus sea freight.

Did this answer your question?