The monitoring of environmental radioactivity is important for public health protection. In France, environmental radioactivity is specifically monitored by a network of certified laboratories. Indeed the Nuclear Safety Authority (ASN) delivers three to five year governmental agreements to each laboratory provided that it succeeds in proficiency tests (PTs) organized by the Institute for Radiological Protection and Nuclear Safety (IRSN). To ensure a direct traceability chain in radioactivity measurements, the Laboratoire National Henri Becquerel (LNE-LNHB), as the French national laboratory for radionuclide metrology, has been organizing national PTs for more than 40 years. LNE-LNHB also regularly realizes specific PTs to train the laboratories to the regulatory tests of IRSN. Most tests are based on aqueous solutions but there is a growing demand for tests on solid matrices to be measured by γ-spectrometry. Measurement of radionuclides from environmental samples includes a wide variety of matrix compositions and densities. Since 2009, LNE-LNHB is working on the production of suitable calibration reference materials to improve the traceability of environmental radioactivity measurements in France. To address this issue, LNELNHB intends to produce mixed γ-ray reference materials with a known mass activity and a composition as representative as possible of real environmental samples. The use of such materials will also improve the calibration of γ-spectrometry measurement systems due to a more accurate determination of the self-attenuation correction by measuring a known sample whose composition is close to the real one. This paper describes the development of the preparation protocol and the characterization of traceable matrices, spiked with various γ-ray emitters. A PT exercise has been organized with a low density matrix produced. The results of the participants are mentioned in this article.