Float test is notoriously unreliable. I wouldn't waste the time. Best thing is to run fingers from tip to root. If it's smooth and squeaks, it low porosity. If it's bumpy, it's high porosity. If it's in between, it's normal.
Drying time is also a good indicator of porosity. My productless hair used to take about six hours to dry after towel drying and diffusing for a bit. I don't have a lot of hair, so that's a fairly long time.
3a (Corkicelli), highlighted, fine, low porosity
modified CG, since April '07
CG since 3/11/08
HGs: Curly Kinks Satin Roots, Curlycue ReNew and Coil Jam; homemade FSG and okra gel; soap bars; DM MiraCurls Curling Gelly; UFD Curly Magic; Shescentit LIs; Sevi conditioners; Botanical Spirits Puree, CJ Repair Me