This blue-emitting plastic scintillator contains natural boron at concentrations up to 5% by weight. It is a clear, stable plastic with physical properties similar to those of the standard Eljen plastic scintillators. Its principal applications are fast neutron spectrometry and thermal neutron detection. The primary function of the boron is to provide a unique scintillation signal for low energy neutrons. The standard formulation contains 5% boron, and practical boron concentrations down to 1% are available.

The isotopic fraction of ¹⁰B in natural boron is 19.9%, meaning that the 5% loaded plastic contains nearly 1% of ¹⁰B. The neutron capture reaction on the boron ¹⁰B(n,αγ)⁷Li  has a Q value of 2.78 MeV of which 2.34 MeV is shared by the alpha and lithium particles. This energy is fully captured in the plastic to produce a scintillation signal approximately equivalent in amplitude to that of a 76 keV electron. For delayed coincidence timing of the capture of fast neutrons, the time delay from the prompt recoil-proton pulse is typically 2.7 μs for 5% B-nat plastics. This delay is inversely proportional to the boron loading.