My first conclusion is that this test took WAAAAY longer than I expected it to! Now if I were a real scientist I would start out by explaining my expectations and the questions I hoped to answer, then my methodology etc etc (boooorrrring!) so instead I'm going to skip straight to what I learned (shhh don't tell my PhD parents!) feel free to scroll down to view all the nitty gritty results, how I got them, and a close up of all the fabrics I tested so you see the visual differences between them.
Conclusion 1: ZORB WINS! (in compression testing)
As I was testing the inserts, I noticed that absorbency doesn't really matter unless the fabric can HOLD ON to what it absorbed. I allowed each insert to drip for 30 seconds prior to weighing but even after that I still wouldn't want anything that sopping wet on my baby's bum. Instead what I cared most about was how the fabric preformed under moderate pressure (15 lbs to be exact) this isn't a lot of pressure and even after each fabric was squished under 15 lbs, there was a LOT of water that I could easily squeeze out with my hands. The purpose was not to put extreme force on the insert but to see how it would hold water under the weight of an average baby. In compression testing, Zorb won, hands down!
Conclusion 2: ZORB WINS AGAIN! (in compression/thickness testing)
Not only was I looking for something that would preform well under moderate compression but I also wanted something that would preform well based on thickness so after I got all of my absorption results, I divided by thickness to get how much a 1" thick insert, made of many layers of a particular fabric would hold. Zorb won again showing that even though the fabric is quite thick, when you correct for thickness it STILL holds more than any other fabric we tested.
Conclusion 3: Zorb/Microfiber wins, and no Zorb did NOT sponsor this test lol! (in cost)
I haven't gathered all the official costs of all the materials yet but Zorb and Microfiber both absorbed the most per layer as well as per inch thick. Oddly, they are also both the cheapest fabrics we tested. Considering they were also the thickest fabrics we tested its safe to say they were ALSO the cheapest per inch thick. I'm not sure which is cheaper, probably microfiber since you can get it anywhere whereas Zorb is only made by Wazoodle but I'll have to run the numbers to find out for sure.
Conclusion 4: There IS room for 2nd place and Hemp (or bamboo) French Terry has it! (In compression/inch thick)
I'll let you scroll down and review the full results yourself to make your own conclusions but MANY moms prefer only all natural fibers, not to mention Zorb CANNOT be used on its own, its a non-woven fabric that needs to be encased in something so if you do use Zorb you will NEED another fabric to sew around it. This means that there is a clear NEED for a second place winner. Although the results point to microfiber being the next best absorbent layer next to Zorb, I wanted to give the 2nd place spot to a natural fiber since many babies do not tolerate Microfiber well. French Terry is CLEARLY that second winner, absorbing about 1.5 ounces more per inch thick than the next best fabric.
Now why did I say hemp OR bamboo french terry gets 2nd place when I didn't TEST bamboo french terry? Well I did test hemp and bamboo fleece and results show that they absorb similarly (bamboo tended to absorb a little more but the bamboo/hemp blend actually absorbed the most of the fleeces) this tells me that the WEAVE of the fabric actually has more to do with absorption than the MATERIAL the fabric is made of. Therefore the french terry in either bamboo or hemp should also absorb similarly. Personally I would go with a bamboo french terry since its cheaper, requires less prep, and is softer!
That's it for my quick and simple conclusions, now the...
Complete data is available via this link, I have summarize the "result highlights" below.
All weights are in ounces, all thicknesses are in inches. For comparison an average baby pees (in ounces) age*2+2 so a 2 year old has a bladder capacity of 2*2+2 or 6 ounces. A 1 year old would have the capacity of be 1*2+2 or 4 ounces. The chart below will tell you how many ounces an insert made of a particular fabric type will absorb, if the insert was made of enough layers to make it 1 inch thick. A 1" thick layer of Organic Hemp Fleece, for instance, would absorb 25.76 ounces in 30 seconds. Although my ounces are measured by weight, they are a rough equivalent for fluid ounces (technically 1 ounce of water weights 1.043 fluid ounces).
Below is a summary chart of the data. To the left of the red line shows absorbency per layer of fabric, data to the right of the red line shows absorbency if all inserts were 1" thick (basically this means I corrected for thickness).
Below is a graph showing absorbency per layer, fabric types are sorted by compression absorbency per layer. (sorted by the GREEN bar)
Below is a graph showing absorbency per layer per inch thick, fabric types are sorted by compression absorbency per layer per inch thick. (sorted by the GREEN bar)
There is one other conclusion I'd like to add, when you look at the chart above you will notice that while there are distinct differences in absorption per inch thick, they are roughly within 20% of each other. Every fabric I tested absorbed pretty well and honestly I'd be happy to use any of these fabrics in my inserts. The main difference is cost, those that were thin to begin with would require you to purchase a LOT more layers to achieve the same absorbency of those that were thicker. Also the natural fibers tend to cost quite a bit more but apparently don't absorb any better. That being said, if someone handed me a stack of free organic hemp fleece inserts, I'd absolutely use them in a heartbeat even though they "technically" got last place - they still absorb pretty darn well!