At one of the big orange DIY shed this past weekend, I ran across a new type of 16-AWG extension cord with a GFCI plug similar to that on some modern hair dryers.
In addition to this, the double-jacketed cord also had a shield around the two conductors in order to detect shorts in the cord thereby tripping the shut-off in the plug.
It came from El Salvador...of all places....
An interesting concept in theory, but picture the average consumer when confronted with the $8 super-smart extension cord versus the equivalent length $1 standard cord from the dollar store. The consumer will almost always go for the $1 cord...
Space heaters EXPLICITLY state that they must not be used with extension cords. It's not only the overheating of the extension CORD that's the problem...it's also the connection between the heater's plug and the extension cord's female connector.
I've noticed heater plug pins tend to heat up a bit. It's not a problem when the thing is plugged into a socket made out of heat resistant plastic like bakelite.
However when you connect the heater to an extension cord -- the typical rubber or flexible vinyl female end will normally get very soft as it gets noticeably hot.
I've done this experiment on 16-gauge extension cords and the even older 18-gauge cords and wound up overheating and damaging the contacts on one of those molded-on rubber female ends.