I was always asked if it is Hawaiian Kapa or Hawaiian Tapa and here is my answer:

In Hawaii, we call the cloth ‘kapa’. In simple terms, the word can mean, ‘the beaten thing’; “ka” meaning ‘the’, and “pa” meaning ‘to strike or hit’. Keep in mind that the Hawaiian language as we know it today was not the same as the language spoken before the arrival of Westerners. At that time, it is very likely that Hawaiian bark cloth was called tapa. The question is, why did all of the Polynesian bark cloth become known as tapa? I have my own theories on this. The Europeans, Russians and Americans at that time did quite a bit of traveling between islands. Between the explorers, whalers, missionaries and the crew, which was often composed of islanders as well, bark cloth was bought and received as gifts or in trade. It is very likely that whichever term was the easiest to remember was the one most commonly used. Hence, after these many years, the word tapa has come to symbolize all Polynesian bark cloth, and the cloth most commonly seen and most widely used even up to these modern times, which would have been the cloths from Samoa, Tonga and Fiji, would be the images that spring first to our minds when the word tapa is used. As a modern day kapa maker in Hawaii, I use the word kapa to create a distinction in people’s minds between our Hawaiian cloth and that of the rest of the Pacific.

Also read, "Differences in Polynesian Kapa/Tapa "