Strength is the second question
Packaging Boxes is the cardboard shop. People often start by asking for a stronger box, when the box in front of them is the wrong shape. A deep carton around a flat book is not solved by double wall. A poster in a cube is not solved by a thicker board. Look at the goods and name the shape: a stack, a flat item, a long roll, a file that will be lifted again, or clothes on a hanger. Then open the range that is that shape.
Board still matters, and the single wall and double wall guide is where that choice is written. Single wall is described as strong, affordable and versatile. Double wall is the stronger board, manufactured in the UK, for heavy, valuable or fragile goods. Make that choice after the shape is right. A strong carton of the wrong proportions still needs fill, still crushes corners, and can still miss a postal size.
A cube when the goods stack
A product that sits as a block wants a carton close to that block. Boxes is the parent of the single wall and double wall cubes, the postal sizes and the specials. Measure the goods, then the carton. If you will reorder the size, write the measurement the way the category prints it, and read measuring a box you will buy again before you rely on a sketch. Internal and external are not the same number. A postal limit is always the outside.
White postal boxes are a finish as well as a size. The white range in stock is described as qualifying as Royal Mail small parcels, in white 125WK/T, including shell-and-slide packs with foam. They are still cubes, or shallow cubes. They are not book wraps. Use them when the outer should be white and the goods are a block that fits the published small-parcel maximum of 450 × 350 × 160 mm on the outside.
A crash lock when the bench is fast
A crash lock box is a style, not only a size. The base locks into shape when the carton is opened, and the range includes a peel-and-seal strip so that seam closes without a separate tape. The category gives the board as 150K/T and describes the boxes as recyclable and biodegradable. It also says they are sized to Royal Mail small parcel guidelines. The sizes listed are 110 × 110 × 95 mm, 160 × 150 × 85 mm, 200 × 100 × 100 mm, 222 × 150 × 88 mm, 290 × 208 × 95 mm and 330 × 220 × 150 mm.
The crash lock guide is the full note. Use this shape when the same small goods go out all day and the packing step has to be short. Do not use it for a heavy stacked load, and do not use it for a flat book. The lock and the strip save time. They do not change the rule about empty space. If the goods rattle, the size is wrong, or you still need a little fill.
A wrap or a tube when the goods are flat or long
Book wraps and M-envelope boxes are flat postal wraps. Book wraps and M-envelope boxes are those ranges, and the book wraps guide explains when a wrap beats a carton. A book, a catalogue or a slim kit that must not be bent belongs in a wrap. Putting it in a cube and surrounding it with paper is more material and a worse fit.
Postal tubes are for a roll: a poster, a plan, a print. The postal tubes guide and the tubes category are that shape. On our Royal Mail page, a roll can still be a small parcel at up to 450 mm long and 80 mm in diameter. A square-box maximum does not describe a tube. If the roll is longer or wider than that, it is a different parcel. Do not fold the poster to make it fit a cube you already have.
Archive and wardrobe are storage shapes
Archive boxes are one-piece A4 cartons with handles and an integral lid, supplied flat. The sides are triple thickness once made up. They are for files and stock you will lift again, not for a one-way postal cube. Archive boxes is the range. A removal or a file store is the job. Sending one as a small parcel is usually the wrong reading of the size.
Wardrobe boxes include a plastic hanging rail for suits, dresses, trousers and jackets. Sizes in that category are internal. Wardrobe boxes is the range, and archive, wardrobe and white boxes keeps the three from being treated as one product. Hanging clothes crease in a cube. Files are a poor fit in a wardrobe box. White postal boxes are neither of those jobs.
Write the shape down, then the board
When a size has worked, the reorder should name the shape first: cube, crash lock, wrap, tube, archive or wardrobe. Then the board, if the range has a choice. Then the dimensions as the category prints them. Then, if it is posted, the outside against 450 × 350 × 160 mm. Box shapes is the index of those ranges on this site.
Orders placed by 3pm leave the same day. UK delivery is free over £50 ex VAT. TradePro, for trade businesses, starts at 5% off and goes up to 10% over £1,000 a month. None of that chooses the shape for you. The goods do. A stronger board, a faster lock or a white finish is a second decision, made after the silhouette of the pack matches the silhouette of what is going inside it.
If you are still unsure, put the goods on the bench and stand the nearest two shapes beside them: the cube and the wrap, or the tube and the cube. The one that leaves less empty air, without bending the goods, is the one to reorder. PayPal branded packaging is a separate finish for sellers who want that outer, not a different shape. Treat it as a printed cube, and still check the size.