GD1 designates a coated secondary fibre board, insert and back grey
(chromo duplex board), top side wood-free white, with special volume (> 1.45 cm³/g).
Front side top layer = hf white
Inlay = grey
Back cover layer = grey
hf white: wood-free white layer of bleached pulp with a maximum of 5% mechanical pulp
grey = layer of recycled pulp (reused cellulose and groundwood fibres)