1. Why Paper Made of Wood Fibers Gets Weak When Wet
Paper is made of wood fibers (cellulose) layered like a net. These fibers are held together mainly by weak attractive forces called hydrogen bonds [1]. Paper has many small gaps and absorbs water easily. When water enters, these bonds weaken, and the sheet loses its strength [1]. It is not that the paper "dissolves"; rather, the connections holding the fibers together loosen. Ordinary tissues tear quickly because they suffer this weakening directly. So, papers designed to be used wet must have some other treatment.
2. How Wet-Strength Chemicals Like PAE Were Developed in 1957
Chemicals that make wet paper strong are called wet-strength agents. A leading example is polyamide amine-epichlorohydrin resin (PAE). According to a review, the first laboratory prototype was made on January 8, 1957, by two researchers at Hercules in the United States [1]. The patent was granted on February 23, 1960. The chemical works by "cross-linking," which chemically connects the fibers to each other. This makes the connections harder to break when water enters. Such chemicals are used in paper products that get wet and dry repeatedly, like towels, tissues, and wipes [2]. However, the specific chemicals used in kitchen paper vary by product.
3. How Thickness and Layering Affect Kitchen Paper Strength
The Fukui Prefecture Consumer Life Center tested 25 brands of kitchen paper in fiscal year 2022. Of the 22 brands that listed their material, 20 were made only of pulp. The remaining two brands, which claimed to be washable and reusable several times, are thought to combine pulp with materials like polypropylene [3]. There were also differences in how they were made. Brands labeled "non-woven fabric" or "felt" had gaps in the surface fibers and thick cross-sections. Brands without these labels often had embossed (raised) patterns on the surface and were often made of two layers [3]. Paper companies also explain that they release products made thicker than existing ones to prevent tearing when wet [3]. The source does not state how much embossing improves wet strength.
4. What Happened When 25 Brands of Kitchen Paper Were Wrung Out
In this test, "resistance to tearing" was evaluated by soaking the paper, wringing it with both hands, spreading it out, and looking at the damage with the eyes. It was not a measurement of strength by pulling with a machine, but a visual scoring [3]. The results showed that 23 of the 25 brands scored between 83 and 100 points. Some brands that did not advertise "tear resistance" still performed well. On the other hand, two brands scored 29 and 46 points, showing a clear difference [3]. Many brands hold up when wrung, but not all are the same. This is a point to remember when choosing at the store or testing at home.
5. Why Wet Paper Is Never as Strong as Dry Paper
Even with chemicals, wet paper does not become as strong as dry paper. One study on bleached hardwood kraft pulp found that wet strength was about 5 to 30% of dry strength [2]. This is a value under special conditions, not a general number for all products. Chemicals also differ in how they work. According to a review, for temporary agents, about two-thirds of the wet strength after 10 seconds of soaking remains after 2 hours, while for permanent agents, 80 to 100% remains. However, this data is for paperboard, and the meaning of "temporary" and "permanent" differs for towels and tissues [1]. In April 2020, Nippon Paper Crexia released a paper towel that can be wrung, washed, and reused like cloth. It is said to have better wet strength than normal kitchen paper, but this is a company announcement with no detailed explanation of the manufacturing process [4].
6. How to Test and Compare Kitchen Paper at Home
If you have two or three types of kitchen paper at home, you can wet them, wring them, and compare how they tear. Soak them in water, wring them gently with both hands, spread them out, and look at where they tore or how holes formed. This follows the same procedure as the Fukui Prefecture test, but since it is a visual comparison, it is not an accurate measurement of strength. Using paper of the same size and soaking them for the same amount of time makes it easier to compare. Look at the surface embossing, thickness, and whether it separates into two layers. If you try this with tissues or toilet paper, the difference may be large. Dispose of the used paper after draining the water, as it is wet. Some products can be used as rags. Comparing labels like "washable and reusable" on the packaging is also a good idea.