A light and stiff fabric woven from bast fibers. In day-to-day conversation asa refers mainly to ramie and hemp-based fabrics. Nowadays most kimono related products made from asa are summer wear (natsumono).
The bast of several different plants are traditionally used in Japan to create fibers for weaving, these include hemp (taima・大麻), ramie (karamushi・苧), kuzu (葛), and basho (芭蕉). Although technically also asa, fabrics made from basho and kuzu are mostly identified by their respective names basho-fu (芭蕉布), and kuzu-fu (葛布).
Asa has a long history in Japan and was the main fabric used before the introduction of cotton. With the arrival of cotton, asa became more of a luxury/specialty product. At the end of the Edo period linen was introduced into Japan, starting local flax cultivation, and adding a new plant based fiber product to the definition of asa.
As a result of restrictions on hemp production/products, asa products are nowadays exclusively made from either ramie or linen.