I just bought a couple of their Thunderbolt™ 5 cables. They seem like a reputable company that would make their cables true-to-spec. Thanks in advance!

This is the one I use and I quite like it. I've had it for a little over a year and a half. I used it to sort (or trash) all my cables and to test new incoming cables.

I bet there's at least one brand with extra–thick plastic insulation.

This already exists. Cable makers can certify their cables and mark them with their data speed and wattage.

I buy only certified, marked cables. If I see an unmarked cable, I assume it’s slow and low-powered…which is good enough for some things.

https://news.ycombinator.com/item?id=47972511