When doing the porosity test, if your hair sinks and then immediately floats back to the top, it is still likely your hair is high porosity. This is because the hair clearly was needing a lot of water. Therefore, the hair absorbed what it needed and then once it had absorbed enough, floated back to the top. Also, if you have hard water, sometimes the minerals in the water can encourage the hair to float to the top more quickly. Because they have a difficult time allowing moisture in, low-porosity strands will not sink.