Despite what you might think the real purpose of the Pee Towel is, it is not actually meant to be urinated on. Instead, it is simply a traditional tea towel with a urine-themed pattern on it. The name itself is a pun on both of these facts.
Created by Amy Rawson, the Pee Towel was inspired by her day job as a lab tech. One of her duties revolves around urinalysis, part of which involves a microscopic examination that is conducted to look for crystal formation. These urinary crystals are a result from a supersaturation of the urine with particular substances that form distinctive shapes, the most common being calcium oxalate. It is this crystal formation that we see on the Pee Towel.