This study reports on the observation of highly confined, low-loss plasmons in graphene–boron nitride (hBN) heterostructures. Using near-field microscopy, the researchers image propagating plasmons in high-quality graphene encapsulated between two hBN layers. They determine the dispersion and damping of plasmons in real space, finding unprecedented low damping combined with strong field confinement. The main damping channels are identified as intrinsic thermal phonons in the graphene and dielectric losses in the hBN. The results show that graphene encapsulated in hBN provides an excellent platform for plasmonic devices due to its low damping and strong field confinement. The study also explores the unique optical and electronic properties of graphene-hBN heterostructures, including altered electronic massless Dirac fermion spectra and tunable propagating phonon polaritons in hBN. The hBN layer provides an exceptionally clean environment for graphene, reducing disorder and enabling the study of optical responses over a wide range of carrier densities. The researchers demonstrate that graphene plasmons in hBN heterostructures exhibit low damping and strong field confinement, with plasmon wavelengths as low as 70 nm, 150 times smaller than free-space light. This represents a record high volume confinement of propagating optical fields. The study quantifies the propagation damping of graphene plasmons, finding that the inverse damping ratio is as high as 25, significantly better than previous studies of unencapsulated graphene. The results show that intrinsic thermal phonon scattering is the dominant damping mechanism, with dielectric losses in hBN contributing significantly. The study also shows that plasmon damping is not affected by carrier density, indicating that the low damping is intrinsic to the graphene-hBN system. The findings demonstrate that hBN is an exceptional environment for graphene plasmons, enabling high confinement and low damping. The results have implications for the development of graphene-based nano-photonic and nano-optoelectronic devices, including single-photon nonlinearities and tunable plasmonic structures. The study provides a detailed understanding of the plasmon dispersion and damping in graphene-hBN heterostructures, paving the way for future applications in plasmonics and nanophotonics.This study reports on the observation of highly confined, low-loss plasmons in graphene–boron nitride (hBN) heterostructures. Using near-field microscopy, the researchers image propagating plasmons in high-quality graphene encapsulated between two hBN layers. They determine the dispersion and damping of plasmons in real space, finding unprecedented low damping combined with strong field confinement. The main damping channels are identified as intrinsic thermal phonons in the graphene and dielectric losses in the hBN. The results show that graphene encapsulated in hBN provides an excellent platform for plasmonic devices due to its low damping and strong field confinement. The study also explores the unique optical and electronic properties of graphene-hBN heterostructures, including altered electronic massless Dirac fermion spectra and tunable propagating phonon polaritons in hBN. The hBN layer provides an exceptionally clean environment for graphene, reducing disorder and enabling the study of optical responses over a wide range of carrier densities. The researchers demonstrate that graphene plasmons in hBN heterostructures exhibit low damping and strong field confinement, with plasmon wavelengths as low as 70 nm, 150 times smaller than free-space light. This represents a record high volume confinement of propagating optical fields. The study quantifies the propagation damping of graphene plasmons, finding that the inverse damping ratio is as high as 25, significantly better than previous studies of unencapsulated graphene. The results show that intrinsic thermal phonon scattering is the dominant damping mechanism, with dielectric losses in hBN contributing significantly. The study also shows that plasmon damping is not affected by carrier density, indicating that the low damping is intrinsic to the graphene-hBN system. The findings demonstrate that hBN is an exceptional environment for graphene plasmons, enabling high confinement and low damping. The results have implications for the development of graphene-based nano-photonic and nano-optoelectronic devices, including single-photon nonlinearities and tunable plasmonic structures. The study provides a detailed understanding of the plasmon dispersion and damping in graphene-hBN heterostructures, paving the way for future applications in plasmonics and nanophotonics.