ENERGY SHELLS. “Strange matter comes about as a way to relieve degeneracy pressure. The Pauli exclusion principle forbids fermions such as quarks from occupying the same position and energy level. When the particle density is high enough that all energy levels below the available thermal energy are already occupied, increasing the density further requires raising some to higher, unoccupied energy levels. This need for energy to cause compression manifests as a pressure.”
https://en.m.wikipedia.org/wiki/Strange_matter