You can buy a special plasticized bag with an address form at a post office, which must be used to send books abroad.

When posting your M-Sack at a post office, you will receive a receipt note
The maximum weight of an M-Sack is 20 kg.
An M-Sack with a written receipt may be sent to any country accepting this service.
If you want your M-Sack to be handled more expediently, request our PLUS (Priority) optional service.