cardboard; paperboard; pasteboard
Refers to thick, stiff paper used for boxes, covers, and packaging. More specific than 段ボール (corrugated cardboard).
This box is made of cardboard.
板紙は包装材として広く使われている。
Paperboard is widely used as a packaging material.
ivory paper
Compound of 板 (ita, 'board') and 紙 (kami, 'paper'), literally 'board paper'. The reading いたがみ is a straightforward combination.