The "Flex-Flesh" was a (toxic free) gelatin substance that you colored with an acrylic and then molded in pre-cast vacuform molds provided in the kit.
It also included greasepaint base colors and shading colors along with relatively good instructions on how to apply them.

It was a lot of fun but there were drawbacks of course.
There was only so much stuff included, so you could only two or three complete makeups.
The edges of the appliances were pretty thick and little chance of blending them successfully into your skin.

Then there was your mom screaming at you because of the mess you made in front of the bathroom mirror.