I use it as a conditioner before I DC.
Porosity Control does help the cuticle to lie flat, but that does not mean it keeps anything "out" of the hair shaft when conditioning. Porosity Control ensures that you have the results you want to have.
Do you want a better relaxer result? Use it before relaxing. Put it in your damp hair (just like the directions say, leave for 30 seconds and rinse). Allow hair to air dry again and then apply relaxer.
* My childhood hairdresser used to do this EVERY TIME he relaxed my hair, and my hair was soooo healthy as a child!!! It never got long because I did so much to it, but it was pretty healthy.
You can use it again after relaxing but before a DC as well.
Do you want your moisturizing conditioner to do what it promised to do? Use PC right before a DC and you will see a major difference in your hair when it is dry and you are styling.
You really do want the cuticles lying flat when you DC or else the moisture goes in and then right back out again. When you make the cuticles lie flat first, the moisture goes in and STAYS IN.
Same for protein. If your hair really needs it badly and you want a good protein condition, PC first and the do the protein condition. Then follow up again with moisture.
Porosity Control simply controls how porous your hair is...making it not so porous. Porous (or open, which leads to dry, brittle hair) is not good.
Those of us with no lye relaxers will REALLY benefit from PC because no lye relaxers make the hair more porous over time than lye based relaxers do.
Naturals benefit the same way....just minus the relaxers of course.
I wrote this because some people were wondering why use PC first when it closes the cuticle. Well, it doesn't
close it per se....it just makes it normal again...flat and ready to receive what you put on it.
I hope this is helpful to those wanting to know.
(PC masters, please correct anything I wrote incorrectly.)
HHG to us all!!!
cj
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Can you say protein overload? 
