This nightgown is called nemaki, literally, sleepwear. At first glance, it looks like a yukata, which is a summer kimono. Traditionally Japanese people wear yukata after bathing or as sleepwear in summer because they are very light and comfortable. This nemaki is even thinner and softer than yukata, and becomes softer with washing. It is made in Japan with high quality cotton, which makes it lightweight, absorbent and a perfect house robe in summer.
If you go to Japan, you might also find the nemaki offered at ryokan, traditional Japanese inns. It is quite refreshing to be in this elegant nemaki after bathing, and drinking cold barley tea on a muggy summer night!