Matrix isolation of molecules was conceived as an efficient experimental technique for studying the structure and reactivity of chemical particles, most often carried out at low temperatures. The idea consists in separating chemical particles (molecules, radicals, clusters, and various transitional states, intermediates) from each other with an inert diluent preventing their interaction with each other and the environment, and thereby allowing one to attribute the results of studies performed, in most cases, with use of spectral methods, to isolated objects. The matrix isolation allows the study of highly reactive molecules that, if not surrounded by the matrix, would immediately enter into reactions or undergo a conversion. The most obvious diluents are inert (or noble) gases Rg = He, Ne, Ar, Kr, Xe. Other popular matrix materials are molecular gases N₂, CO. In recent years, the molecular hydrogen H₂ has been attracting attention as a matrix material. At low temperatures (around 10 K), these substances can be converted into a more or less ordered solid phase, and the spaces between the lattice sites can accommodate extraneous molecules. The matrix lattice acts as a "host", and the introduced (or matrix-isolated) molecule acts as a "guest" in the resulting complex system. Technically, the matrix is formed by depositing on a cooled substrate a flow of inert carrier, i.e. the matrix material, which entrains the flow of a substance supplying the matrix-isolated molecules. For obtaining the gas flow of future matrix-isolated molecules the corresponding substance is evaporated either thermally or by laser irradiation.

In a broader sense the term "matrix" can refer to much more complex structures than those mentioned above. For example, well known interstitial compounds of graphite, in which clusters of alkali metals (matrix-isolated particles) are introduced between the graphite layers (matrix). Another class of interstitial compounds is formed from liquid crystals incorporating metal particles.

Of growing importance lately is the synthesis of nanoparticles in different form factors (from globules to nanoplates and nanowires) that is carried out in one- or two-dimensional reactors and results in nanocomposites, in which the nanoparticles are separated from each other and the environment by the matrix walls, which prevent their chemical interactions and changes in functional properties.