It's called cardboard, but I haven't bought it online. Personally, I think the smooth surface is not suitable for flat construction, because the smooth surface is easy to rub flowers, and the back is a little yellow and not white enough, so it is not easy to produce results. I think double-sided white cardboard is not only white, but also very practical and smooth. I feel that these two kinds of paper should not be difficult to find online. Please have a look again.