These mats are made of Igusa - in daily lingo its "Juncus effusus L. var. decipens Buchen." Tatami mats are also made from Igusa. In the Summer, we stick one over our futon (bed) to keep us cool and it also helps keep the sweat from seeping into the futon.
These Totoro ones cost between
5980 yen and
8980 yen depending on the size. They can be rolled up so if you are thinking of buying one then you should have no problem sticking it into your suitcase or as a carry on.