Can Thermal Imaging Cameras See Through Walls?

The answer is no. Wall materials such as brick, concrete, wood, and drywall block infrared radiation. Thermal cameras can only detect the temperature of the wall’s surface and cannot obtain information about what’s inside.

Although infrared thermal imagers cannot see through walls, if there are temperature differences within the wall (such as due to water leaks or missing insulation), heat will conduct to the surface, creating temperature variations. Thermal imagers can capture these temperature differences, thereby indirectly detecting wall defects and pinpointing problem areas.

The following substances exhibit high absorption or reflectivity in the infrared spectrum, blocking the transmission of infrared radiation and preventing infrared thermal imagers from “seeing through” them:

Generally, ordinary glass is almost entirely opaque to long-wave infrared radiation. Therefore, conventional thermal imagers cannot see through regular glass to observe objects behind it. However, certain specialized types of glass possess good transmissivity to specific infrared wavelengths, depending on the glass type, thickness, and the operating waveband of the infrared thermal imager. For example, while ordinary glass is almost completely opaque in the long-wave infrared range, it has higher transmittance in the short-wave infrared range. Objects behind such glass can be observed using short-wave infrared thermal imagers. Consequently, in practical applications, it’s crucial to select the appropriate thermal imager configuration based on specific needs and to consider the influence of the glass material and any surface treatments.

Infrared thermal imagers cannot see through metal objects. However, they can indirectly analyze internal structures or defects by detecting the temperature distribution on the metal’s surface. It’s important to note that smooth or polished metal surfaces highly reflect infrared radiation from the surroundings. Directly measuring the temperature of such surfaces can lead to inaccurate readings due to the reflected heat. In contrast, oxidized metals (like rusted surfaces) or metals coated with matte materials are easier to measure accurately.

Wood strongly absorbs and blocks infrared radiation, particularly in the far-infrared spectrum. Consequently, infrared radiation struggles to penetrate wood. However, under specific conditions, anomalies in the temperature distribution on the wood’s surface can be detected to indirectly infer thermal abnormalities or structural issues within the wood. For example, internal voids, cracks, insect infestations, or damp areas within the wood can affect its heat transfer properties, leading to unusual temperature changes on the surface.

While infrared thermal imagers cannot directly see through paper, if the paper is very thin and the temperature of an object behind it is conducted to the paper’s surface, the thermal imager can indirectly display the object behind. For example, when a hand is placed on the back of a sheet of A4 printer paper, the thermal imager can show the temperature distribution on the paper’s surface resulting from the hand’s heat being conducted through it, rather than directly detecting the hand’s temperature.

Thick plastics or those with additives that block infrared radiation will hinder the penetration of infrared radiation, preventing thermal imagers from seeing through them. However, certain thin plastic materials (such as polyethylene film) exhibit some degree of transparency to infrared radiation, especially in the mid-wave infrared and near-infrared bands, allowing thermal imagers to detect heat sources behind them. Therefore, whether an infrared thermal imager can see through plastic depends on the type and thickness of the plastic, as well as the imager’s operating waveband.

Whether infrared thermal imagers can see through clothes is a common concern. Infrared thermal imagers cannot directly penetrate clothing and reveal human body details like X-rays. However, in certain situations, they might show the outline of a person under their clothes. For example, some lightweight materials or those with higher infrared transmittance may allow some infrared radiation to pass through, enabling the thermal imager to display the heat distribution patterns underneath the clothing under specific conditions, creating a “see-through” effect.

Infrared thermal imagers cannot directly “see through” the internal structures of the human body. However, they can indirectly indicate health issues by detecting changes in body surface temperature. Medical infrared thermal imagers primarily work by detecting abnormal surface temperatures that reflect physiological changes such as metabolism, blood circulation, or inflammation. This is an indirect method of detection and does not constitute true “seeing-through.” It cannot display the anatomical structure of internal organs or deep pathological changes.

Certain substances exhibit higher transmittance in specific infrared wavebands, allowing infrared thermal imagers to “see through” them in these ranges:

Infrared thermal imagers can penetrate smoke and fog under certain conditions, primarily due to their ability to detect long-wave infrared radiation. Compared to visible light, long-wave infrared has a stronger diffraction capability, enabling it to bypass the tiny particles in smoke and fog, reducing the effects of scattering and absorption. This allows for the imaging of obscured objects. Consequently, infrared thermal imagers are widely used in firefighting, search and rescue, security, and other fields to detect heat sources and identify targets in low-visibility environments.

One of the most significant advantages of infrared thermal imagers is their ability to produce clear images in environments without any light. Their imaging principle relies on detecting the infrared radiation (heat radiation) emitted by objects themselves, rather than depending on external light sources for illumination. Therefore, even in completely dark environments, as long as there is a temperature difference between a target and its surroundings, an infrared thermal imager can “see” it. 

Thin plastic materials such as cling film and plastic bags, when sufficiently thin, allow infrared radiation to pass through them, enabling thermal imagers to detect heat sources behind them.

Different types of glass have varying degrees of transparency to infrared radiation. Whether an infrared thermal imager can see through glass to observe objects behind it primarily depends on the type and thickness of the glass, as well as the waveband selection of the infrared thermal imager being used. Certain glass materials exhibit good transmittance in specific infrared wavebands, allowing infrared thermal imagers to “see through” them. Examples include:

· Quartz Glass: Has high transmittance in the short-wave infrared band. If it’s necessary to observe objects behind quartz glass, a short-wave infrared thermal imager should be selected.

· Germanium Glass: Exhibits good transmittance in the mid-wave and long-wave infrared bands and is commonly used as window material for infrared thermal imagers.

· Chalcogenide Glass: Possesses excellent infrared transmission properties, performing particularly well in the mid-wave and long-wave infrared bands. Consequently, chalcogenide glass is often used to manufacture lenses, windows, and other optical components for infrared thermal imagers.

Tags: Thermal Camera, Thermal Imaging Camera, Infrared Imager