Mailer Box Inserts: Types, Materials and When You Need One

When do you need a mailer box insert?

You need an insert when the product can move inside the box, when several items could hit each other, or when presentation on opening matters. If the product fills the box snugly on all sides, or is soft and hard to damage, like folded apparel, an insert usually adds cost without adding protection.

Decision rules that work in practice:

• Glass, ceramics, candles in jars, bottles, electronics and anything with a fragile corner: insert needed.
• Two or more items in one box, especially mixed sizes: partitions or a cradle stop them colliding.
• One box size used for several products: an insert (or a set of inserts) locates each product without needing a new box.
• Subscription and gift boxes where the opened lid is the brand moment: an insert controls how products sit and look.
• Flat, rigid products that already fit the box: no insert; size the box correctly instead (see mailer box sizes).
• Textiles, soft goods and unbreakable items: usually no insert; tissue or a printed card if presentation matters.

Which types of mailer box inserts are available?

The main options are die-cut corrugated inserts, folded board partitions, moulded pulp trays, paper void fill and foam. They differ in how firmly they hold the product, whether they need tooling, how long they take to pack and whether they stay in the same recycling stream as the box.

Die-cut corrugated inserts

The most common choice for printed mailers. A flat blank is cut and creased from corrugated board, usually E or B flute, then folded into a cradle, a raised platform with cut-outs, or a frame that holds the product away from the walls. Using the same board family as the box keeps the whole pack in one paper stream. The flute direction and caliper matter: a cut-out in a thicker flute holds a heavy bottle better, while thinner flutes give cleaner edges for visible inserts. Board choice for the box itself is covered in corrugated board grades for mailer boxes.

Folded board partitions and dividers

Interlocking slotted partitions or folded divider strips split the box into cells. They suit sets of bottles, jars or tins of the same size and are what most searches for "boxes with dividers" mean. They separate items well but give little cushioning against a corner drop, so heavy glass usually needs partitions plus a box grade with enough rigidity.

Moulded pulp trays

Moulded pulp is formed from wet fibre on a shaped mould and dried, so it can follow a product's contour closely. It holds irregular shapes better than anything die-cut from flat board and cushions well. The trade-offs are a mould cost that typically sits above a cutting die, a more natural surface that is harder to print, and a longer path to a first sample. It makes most sense for stable, high-volume products whose shape will not change for some time.

Paper void fill

Crinkle paper, crumpled kraft and paper cushioning are fast to start and flexible across mixed orders. They do not fix the product in place, so items can migrate to a wall or corner during transit. Under the PPWR, filling materials count as empty space, which matters for e-commerce packaging from 2030 at the earliest (see below).

Why avoid foam and plastic inserts where possible?

Foam protects very well, but it turns a paper-based pack into a mixed-material pack. The customer has to separate the foam, many household collections do not take it, and it complicates recyclability claims and future EU recyclability grading. For most products a corrugated or moulded pulp insert can be designed to give adequate protection.

The specific issues:

• Recyclability. From 1 January 2030 (or 24 months after the design-for-recycling delegated acts, if later), PPWR Article 6 requires packaging to meet recyclability grade A, B or C, and from 2038 grade A or B, with EPR fees modulated by grade. A mono-material corrugated pack is expected to be well placed; a corrugated box with a foam insert has two materials to assess and separate.
• Empty space. PPWR Article 24 names foam fillers, polystyrene chips, air cushions and bubble wrap among the filling materials that count as empty space.
• Claims. A "plastic-free" or "fully recyclable" pack claim is not available if a foam insert is included.
• UK Plastic Packaging Tax. Plastic packaging components with less than 30 % recycled plastic are taxable for UK manufacturers and importers above the registration threshold, and inserts are packaging.

Foam still has a place for high-value, shock-sensitive items such as instruments or premium electronics, particularly where the pack is returned and reused. If you use it, document why paper-based alternatives were not adequate; that rationale is useful under the PPWR minimisation rules.

How do you design an insert to fit the product?

Start from the packed product, not the catalogue dimensions. Measure the item as it ships, including its own carton, sleeve or wrap, measure several units to see the variation, and design the cut-outs with a small clearance so the product drops in without force but cannot rattle.

Points that decide whether an insert works:

• Product tolerances. Bottles, jars and moulded products vary between batches and suppliers. Design to the largest measured unit plus clearance, and check the smallest still sits firmly.
• Board caliper. Corrugated board has real thickness, so a fold or a cut-out edge eats into the internal space. The structural designer works this into the dieline; supply internal dimensions and let them handle the allowances.
• Orientation. Decide which way up the product travels and which face the customer should see first. Liquids and pumps usually travel upright.
• Distance from the walls. The insert should keep fragile surfaces away from the box walls and corners, where impacts arrive.
• Interaction with the box. Box and insert are designed together: the insert sets the box's internal dimensions, and the box's closure must not press on the product.
• Range planning. One box with different inserts for several products can reduce box variants, while one insert used across several products usually protects none of them well.

Confirm the design on unprinted white samples with real products before ordering production tooling. How dielines, cutting dies and structural samples work is covered in carton dielines, cutting dies and structural prototyping.

How does an insert protect against drops and vibration?

An insert protects in three ways: it immobilises the product so it cannot build up speed inside the box, it keeps the product away from the walls and corners where impacts land, and it provides a zone that can crush or flex to absorb part of the energy. Most breakage in parcel networks comes from drops and from items moving and rubbing during vibration.

• Drops. The box hits the floor on a face, edge or corner. Corner drops are the most damaging for glass. Raised platforms, corner blocks and cradles that suspend the product leave a crush zone between product and impact point.
• Vibration. In vans and on conveyors, loose products shuffle, scuff printed surfaces and loosen closures. A snug fit stops this; void fill only reduces it.
• Compression. Stacked parcels press on the lid. An insert that supports the top panel near the product helps, but stacking strength comes mainly from the box board grade.

Test with real products and real fill levels. Parcel-shipping test procedures from ISTA, such as the 3-series for parcel delivery systems, are commonly used to simulate drops and vibration, and some marketplaces have their own packaging requirements. A few rounds of simple drop tests on samples often show the weak point before production.

How do inserts affect the PPWR empty space rule?

Under the PPWR, Regulation (EU) 2025/40, Article 24, the economic operator that fills e-commerce packaging must keep the empty space ratio at no more than 50 %, from 1 January 2030 or three years after the Commission's methodology act, whichever is later. Filling materials such as paper cuttings, air cushions, bubble wrap and foam fillers count as empty space.

That is the regulatory case for fitted inserts. A box sized to the product with a fitted insert has less space to fill and typically less loose fill to count. Exactly how a fixed insert is treated in the calculation will be set out in the methodology act, so do not assume an insert counts as product volume. Article 10 on minimisation, also from 2030, adds that packaging weight and volume should be reduced to the minimum necessary for function, and specifically targets features meant only to increase perceived volume, such as false bottoms and unnecessary layers. An insert that raises a small product to fill a large box for show is the kind of design to avoid.

The calculation, who is responsible and a worked example are covered in e-commerce packaging and the PPWR.

What does a custom insert cost?

An insert adds a one-off tooling cost and a unit cost. For die-cut board inserts, the cutting die is usually the main one-off item; for moulded pulp, the mould. Unit cost depends on board grade, blank size, how many blanks fit on a sheet and any gluing or pre-folding.

Ways to keep insert cost down: design inserts from the same board grade as the box, keep blanks compact so they nest well, reuse one insert design across products that share a footprint, and avoid features that need gluing unless the time saving at packing justifies it. How tooling is spread across order quantities is covered in packaging cost drivers and packaging MOQ.

How much packing time does an insert add?

It depends on the design. A flat card platform or a moulded pulp tray drops in within seconds; a multi-fold cradle that has to be erected and locked can take longer than the box itself. Compare total bench time per order, including void fill you no longer need, not just the insert.

Ask the fulfilment team to time samples on the real bench. Two or three seconds per order adds up over a high-volume range, and an insert that is quick to pack is more likely to be used correctly.

Can mailer box inserts be printed?

Yes. A printed insert is often a cheaper route to an unboxing moment than printing the whole inside of the box, because the insert is a smaller blank and the product sits on the printed surface. One-colour flexo or digital printing is common, and a logo or short message on the platform around the product is usually enough. The trade-offs between inside print, printed inserts and insert cards are covered in inside printing and unboxing design for mailer boxes.

What makes an insert a mono-material paper solution?

An insert is mono-material in practice when it is made from paper or board, carries water-based inks if printed, and has no plastic lamination, foam pads, plastic windows or self-adhesive plastic elements. Paired with a corrugated mailer, the whole pack can then go into one paper and card stream without the customer separating anything.

Small details decide this. A foam strip glued to a corrugated cradle, a film-laminated platform or a plastic tie to hold a product creates a second material. Where extra grip is needed, a tighter cut-out, a locking tab or a paper band usually does the job. Moulded pulp and corrugated inserts can also be combined, since both are fibre-based.

What to send when specifying a mailer box insert

• Product dimensions and weight as packed, measured on several units, plus photos
• How many products per box and which combinations ship together
• Fragile points (corners, pumps, glass necks, screens)
• Orientation and the face the customer should see first
• Box style and internal dimensions, if the box already exists
• Insert type preference, or "open to proposal"
• Print requirements for the insert, if any
• Annual volume and how many product variants share the box
• Packing method: manual bench, semi-automated line
• Target markets, for PPWR, EPR and recyclability considerations

Send this with the box specification through the custom printed mailer boxes page, or contact 9 Packaging with samples of the product. Insert structure, board and tooling are confirmed during quotation and technical review, usually after a white sample has been checked with the real product.