Measure before you open the range
Choose double wall for the weight or the stack, then the size. Do not choose it only because it sounds safer for a light item.
Double wall is the stronger board, made in the UK, for heavy, fragile or stacked goods. The page for Double wall boxes is where Packaging Boxes shows that line.
The published limit, if there is one
The range is also the removal board. It is listed apart from single wall.
A larger single wall carton adds air and still has the lighter board.
Write the size down
Say double wall and the size.
On Packaging Boxes, put Double wall boxes on the order with the lines it belongs to, so you are not paying a second delivery for the piece you forgot. Free UK delivery starts over £50 ex VAT.
Open Double wall boxes when you already know this line. The bundle quantity is on the page. Packaging Boxes will still dispatch an order placed by 3pm on the same day.