I did not know the answer to this question, but I was in the lab when I saw it and decided to do an experiment to find out. You could probably do a similar experiment at home. I used a simple paper towel that we have in the lab, not a brand name product. I weighed it - it weighed 2.2 gram.

I then added water, which the paper towel started to absorb. I kept doing this, making sure to wet the paper towel easily. A somewhat tricky question is how to decide when the paper towel stops absorbing.

I decided for my experiment that I would consider that the paper towel had absorbed all the water it could once there were no dry spots on the paper towel and some droplets of water would remain on the scale as I picked up the paper towel (I did the adding of water while the paper towel was on the scale). This point came when I had added 4.4 grams of water (the same as 4.4 mL, because the density of water is 1 g/mL).

So the paper towel absorbed twice its weight in water, which I found quite impressive. If you want to do a similar experiment, maybe with different brands of paper towels, at home, you may want to use many paper towels at once so that you can use a kitchen scale. It could also be interesting to compare paper towels to a diaper, which will absorb many more times its weight of water.