In physics, a perfect fluid or ideal fluid is a fluid that can be completely characterized by its rest frame mass density and isotropic pressure ⁠⁠. Real fluids are viscous ("sticky") and contain heat. Perfect fluids are idealized models in which these possibilities are ignored. Specifically, perfect fluids have no shear stresses, viscosity, or heat conduction. A quark–gluon plasma and graphene are examples of nearly perfect fluids that could be studied in a laboratory.