A Simple Shower Test for Evaluating Backpack Water Resistance

Nice, but what is the practical use for the average backpacker?

Interesting, a couple things about the test. You use Rating Categories based upon visual observation yet, you measure the weight gain. This seems odd that you are using qualitative information for ratings yet include quantitative. It seems that quantitative measures would be better.

You have weight gain of the pack but do not infer a relationship to Rating Categories. This seems odd as the only mechanism to get water into the pillowcase is through the pack. Wouldn’t there be a water flow resistance in series?

Weight is the pillow is interesting. It would be great to know the full capacity of the pillow. If it could store 1000g that is one thing, if it can only store 150 g then you maxed out your metric. Lastly, absorption metrics can be tricky as water in the pillowcase is based upon capillary action. Measure the pillowcase flat and that would be the highest capacity. Holding in vertically, you may lose a lot of water because of the static head (if that makes sense). A quick check would be to add dye to the water and dip the dry pillowcase into the fluid see how high the fluid wicks vertically.  My 2 cents.