Paper
iDEALS UK PACKAGING LTD White C5 A5 size large letter postal mailing cardboard boxes 229mm x 159mm x 20mm - 9'' x 6.3'' x 0.8'' (200)
This size box has been designed to meet the new pricing structure set by the postal services. These boxes qualify as Large Letters. Internal size: 23cm x 16cm x 2cm, external size: 24.5cm x 16.5cm x 2.4cm Strong and sturdy but light so they don't...
https://www.bizrate.co.uk/paper/ideals-uk-packaging-ltd-white-oid25764018208.html