This pattern is essentially a recipe for an alternative for a reenforced heelflap. It can be applied in any pattern that uses a traditional heelflap.
The result is a sturdier, slightly less stretchy heelflap.

This is a pattern for sock madness 16.
It is available and downloadable to everyone now that sockmadness 16 has ended.

https://ravel.me/hxln3a : a search for free sock madness patterns with a heelflap