Since about 19986, Starting with DPF, there has always been panties on the market called "Tuffy". The usually has been characterized by material greater than 5 mil aka "gauge" thick. Babykins https://www.myprotex.com/collections/vinyl-plastic-pants-for-adultshas "6 mil Tuffy" and MyProtex is no different. I cannot speak to the Tuffy II line as a whole
Because they have, at the moment, which is the watchword in the world of rubber panties, 3, blue and white in 7 mil and a clear in 8 mil.