As a result, current research into military materials is increasingly focused not only on fabric composition or emissivity, but also on surface microtexture. What appears to the human eye as an almost smooth surface is, from the perspective of infrared radiation, a complex geometric structure that governs the emission, absorption, and reflection of thermal energy. In other words, two fabrics with the same emissivity can exhibit substantially different thermal imaging signatures solely because of differences in their surface microstructure.<\/p>\n
Why thermal imagers do not actually “see” temperature<\/h2>\n
One of the most common misconceptions is that a thermal imager measures an object's temperature directly. In reality, modern thermal imaging systems detect the intensity of infrared radiation reaching the detector array.<\/p>\n
That signal is simultaneously influenced by several factors:<\/p>\n
- \n
- surface temperature;<\/li>\n
- the material's emissivity;<\/li>\n
- the reflectance of ambient infrared radiation;<\/li>\n
- surface geometry;<\/li>\n
- the sensor's spectral range;<\/li>\n
- the viewing angle;<\/li>\n
- atmospheric conditions.<\/li>\n<\/ul>\n
The last three factors are often underestimated when developing camouflage materials.<\/p>\n
As early as the 1970s, American researcher Fred Nicodemus demonstrated that the reflection characteristics of any surface can be described by the Bidirectional Reflectance Distribution Function (BRDF)<\/a>. This concept was later extended to the thermal radiation emitted by surfaces. For military applications, the implication is straightforward: thermal detectability depends not only on how much thermal energy a material emits, but also on the directions in which that energy is emitted<\/a>.<\/p>\n
![\"\"](\"https:\/\/stg-defence.com\/wp-content\/uploads\/2026\/08\/vpliv-mikroteksturi-1-450x253.png\")
<\/p>\nMicrotexture as a means of controlling the direction of thermal radiation<\/h2>\n
At the microscopic level, any fabric consists of countless fibers, weaves, pores, surface irregularities, and microscopic protrusions. Each of these elements interacts with infrared radiation. If a surface is perfectly smooth, a significant portion of the thermal energy is emitted in a well-defined direction. In such cases, the thermal imager receives a high-contrast signal.<\/p>\n
However, as surface micro-roughness increases, this behavior changes significantly. Each microscopic irregularity acts as an individual scattering element: part of the energy is reflected, part is absorbed, and part undergoes multiple internal reflections between neighboring structures before being re-emitted in different directions. As a result, the thermal energy is distributed across a much wider range of directions, reducing the intensity of the signal that reaches the thermal imager directly. This is why two fabrics at the same temperature can appear completely different in a thermal image.<\/p>\n
![\"\"](\"https:\/\/stg-defence.com\/wp-content\/uploads\/2026\/08\/vpliv-mikroteksturi-2-450x407.png\")
<\/p>\nThe microcavity effect<\/h2>\n
One of the most intriguing phenomena in modern infrared physics is the microcavity effect<\/a>. When a surface has a complex relief with numerous microscopic cavities, thermal radiation interacts repeatedly with the walls of these microstructures. As a result, some of the photons are:<\/p>\n
- \n
- reabsorbed;<\/li>\n
- re-emitted;<\/li>\n
- redirected.<\/li>\n<\/ul>\n
![\"\"](\"https:\/\/stg-defence.com\/wp-content\/uploads\/2026\/08\/vpliv-mikroteksturi-3-450x410.png\")
<\/p>\nAs a result, the thermal signal leaving the surface in the direction of the thermal imager becomes weaker. This principle is widely used in the development of low-emissivity coatings, infrared absorbers, radar-absorbing materials, and modern multispectral camouflage systems.<\/p>\n
It is important to understand that this is not about insulating heat. The material does not trap heat inside; rather, it modifies the way thermal radiation is emitted into the surrounding environment.<\/p>\n
Why smooth materials often perform poorly in the thermal spectrum<\/h2>\n
At first glance, it may seem that an exceptionally smooth surface should be less detectable. In reality, the opposite is often true. Smooth surfaces exhibit several characteristic drawbacks, including pronounced specular reflection, strong sensitivity to the viewing angle, localized hot spots, and increased thermal contrast. These effects become particularly noticeable when viewed by a thermal imager at shallow angles or when the surface is exposed to solar radiation.<\/p>\n
This is especially relevant for:<\/p>\n
- \n
- metal vehicle structures;<\/li>\n
- plastic UAV components;<\/li>\n
- untreated synthetic fabrics;<\/li>\n
- equipment with smooth surface coatings.<\/li>\n<\/ul>\n
For this reason, modern military solutions increasingly avoid completely smooth outer surfaces. Instead, they incorporate a controlled microrelief that promotes more diffuse thermal emission.<\/p>\n
The correlation between surface microtexture and emissivity<\/h2>\n
Technical literature often describes emissivity (\u03b5) as the primary property of a material. However, this represents only part of the picture. Actual infrared detectability is determined by a combination of several factors:<\/p>\n
- \n
- spectral emissivity;<\/li>\n
- the spatial distribution of emitted radiation;<\/li>\n
- surface roughness;<\/li>\n
- microstructure geometry;<\/li>\n
- the material's polarization properties;<\/li>\n
- the wavelength range in which the sensor operates.<\/li>\n<\/ul>\n
Studies conducted by NASA, Sandia National Laboratories, and several universities have shown that modifying a surface's microtexture can significantly alter its infrared signature without changing the material's chemical composition<\/a>. This is because surface geometry determines how thermal radiation is emitted in different directions and across different spectral bands.<\/p>\n
One of the most illustrative examples of engineered surface microrelief is the biomimetic approach \u2013 using mechanisms found in nature to develop advanced camouflage materials. Numerous organisms, including butterflies, beetles, desert reptiles, marine mollusks, and certain plant species, possess complex hierarchical surface microstructures that regulate interactions with light, moisture, and thermal radiation.<\/p>\n
For military developers, this has become a fundamental design consideration. Whereas the primary focus once lay in selecting materials with appropriate emissivity, increasing attention is now being devoted to engineering surface structures at the micro- and even nanoscale. By combining material composition, surface architecture, and specialized coatings, it is possible to develop multispectral camouflage systems in which engineers replicate complex hierarchical structures that function across the visible, near-infrared, and thermal infrared spectral ranges.<\/p>\n
Fiber, weave, and surface microrelief \u2013 three levels of thermal signature control<\/h2>\n
While surface microtexture determines how thermal radiation leaves a material, the internal structure of the fabric is equally important. From the perspective of infrared physics, a textile is a complex multilayer system in which every structural level influences heat transfer processes.<\/p>\n
Three levels of thermal signature formation<\/a> can be distinguished:<\/p>\n