Cardioid and hypercardioid patterns
To produce the in-between polar patterns one could consider the omnidirectional microphone where the diaphragm is open on one side only, and the figure-of-eight microphone where the diaphragm is completely open on both sides.
Allowing partial access only to one side of the diaphragm would therefore seem to be a viable means of producing the in-between patterns, and indeed it is.
A cardioid or hypercardioid mic therefore provides access to the rear of the diaphragm through a carefully designed acoustic labyrinth.
Unfortunately the effect of the acoustic labyrinth is difficult to equalize for all frequencies, therefore one would expect the polar response of cardioid and hypercardioid microphones to be inferior to that of omnidirectional and figure-of-eight mics.