Rick,
You have some excellent science in your reply.
I can’t find it but someone has cut open a First Need Cartridge. It looked like something like volcanic ash; completely homogeneous. Thus if it did crack, it will let dye through and probably everything else. It appears to be an elegant concept. 25+ years of experience sounds like it is one of the few models that have withstood the test of time.


It was nice for First Need to publish unbiased studies of their product. I can’t find studies on MSR’s sight.

I’ve been using First Need for about 6 years. Last Feb was the first time I caught a cartridge that let the blue through. It so happened, it went below freezing that night. We were snowed on. If I was paying attention, I would have brought the filter into my sleeping bag.

The hyperflow has a good idea to see if it’s cracked. What I read last year (and maybe it has changed) is to see if bubbles come up. However, in practice, it seems all filters let out a few bubbles under water. Thus how would you differentiate the OK bubbles from the oh-no-the-filter-cracked bubbles? Also, it seems like several hollow fiber tubes have to crack before the naked eye can start discerning bubbles.

-Barry