I'm doing a project where I need some filters. I found some reasonably priced ones on the internet but I have no idea how to tell which size is which. I'm looking for the size that filters out the smallest particles. The sizes available are 0.45 microns and 0.2 microns. I know this may seem like a pretty dumb question but which way do these numbers go, it seems to me that the 0.45 micron filter would be the finest one. I'm lost in space on this one & need to get the filters soon. If anyone can help I would appreciate it. THANKS!!!