Used indoors for 10 years, used for stair handrails. Has some warping and small holes. Will be thoroughly cleaned before shipping. This is plastic corrugated cardboard, which is strong against impact and has excellent insulation and soundproofing properties. Unlike paper cardboard, it can be used repeatedly, making it economical. Ideal for protecting buildings during moves and relocations, as display boards, or for craft materials. IRIS Ohyama Plastic Corrugated Cardboard 910X910X4 Natural PD994NT Available on Amazon in a [5-sheet pack] for 4400 yen. A great deal for those who don't need five sheets.