No. Thermal can’t see through glass, walls or water, because all three block the long-wave infrared energy a thermal sensor reads, so you see the temperature of their surface instead of whatever is behind it. Fog, rain and smoke work differently: they absorb and scatter part of that energy on its way to you, so a thermal image often keeps working in bad weather with less range and contrast, though dense fog can leave you without a useful image.

Many people find this out the first time they scan from a truck cab or through a cabin window and the screen shows nothing useful. Below we go through each material, then the weather, then what it means for the way you scan with a thermal monocular or riflescope.

What a Thermal Sensor Actually Reads

A thermal device doesn’t look through things. It measures the infrared energy coming off the surface of whatever is in front of it, and that signal mixes what the surface emits with what it reflects from its surroundings, as the overview of thermography explains. Most thermal cameras work in the long-wave infrared band, roughly 7 to 14 micrometers.

That band behaves very differently from visible light. Some materials your eye sees straight through stop it, and some that look solid let much of it pass. So the useful question is not “can I see through it?” but “does long-wave infrared get through it?”

The materials in this table either block the infrared from what is behind them or let it through. Weather absorbs and scatters that infrared along the way, and dense fog can stop a useful image altogether. Keep those two groups apart and most thermal surprises make sense.

Can Thermal See Through Glass?

No. Ordinary glass lets visible light through but blocks long-wave infrared. This has been known for centuries: in 1681 Edme Mariotte showed that glass, though transparent to sunlight, obstructed radiant heat. A well-known comparison photo on the Infrared page shows it in one frame: a man’s eyeglasses look opaque in the thermal image, while a plastic bag over his arm is mostly see-through.

Point a thermal device at a window and the screen shows two things:

• The glass’s own surface temperature. You read the pane, not the room, the person or the animal behind it.
• Reflections. Glass can reflect infrared from warm things in front of it, so you may see a faint image of yourself, a lamp or a running engine.

This is also why the front lens of a thermal camera isn’t made of ordinary glass. Germanium is transparent in the infrared, and it is used as the front optic of thermal imaging cameras that work in the 8 to 14 micron range.

In the field, a windshield, a closed cabin window or a glass door ends the scan. Lower the window or step outside.

Can Thermal See Through Walls?

No. Walls, doors and other solid building materials block long-wave infrared, so a thermal device reads only the surface temperature of the wall. A person or animal standing on the other side does not show up.

What can show up is anything that changes the surface temperature of the wall. Building inspectors use thermal cameras to find heat leaks where insulation is faulty and to spot moisture in walls and roofs, because those problems leave warmer or cooler patches on the surface. They aren’t seeing inside the wall; they’re reading the pattern it leaves on the outside. We cover that use in our guide to detecting hidden moisture behind drywall.

For hunters and landowners the practical version is simple. An animal inside a barn, a culvert or a hollow log is invisible to thermal until part of it is in the open.

Can Thermal See Through Water?

No. Water absorbs infrared so strongly that a thermal image of a pond or river is a map of the very top of its surface. Satellite instruments that measure ocean temperature in the infrared run into the same limit: the reading comes from the top “skin” of the water, about 0.01 mm or less, as the sea surface temperature overview describes.

So thermal shows you whatever breaks the surface, such as a swimming animal’s head and back or ducks on open water. Anything fully under water stays hidden, which is why thermal is a poor tool for finding fish. We explain what it can and can’t do around water in Can You See Fish with a Thermal Scope?

What Thermal Can Partly See Through

Thin Plastic

Some thin plastics let much of the long-wave infrared through. In the comparison photo above, the plastic bag is mostly transparent. Motion sensors rely on the same effect: infrared reaches the sensor through a plastic window that may look cloudy to the eye. How much gets through depends on the plastic and its thickness, so treat it as a curiosity rather than something to plan around.

Leaves, Grass and Brush

Leaves and grass are surfaces like any other, so thermal doesn’t see through them. What it picks up is heat coming through the gaps between them. An animal in thin cover often shows as broken patches, such as an ear, a strip of back or part of a head between branches. Dense, leafy cover can hide it completely.

If a shape looks broken up, move a few steps to change your angle before you decide what it is.

Fog, Rain and Smoke Are a Different Problem

Weather works differently from a wall. Fog, rain and smoke are droplets and particles spread through the air between you and the animal. They absorb and scatter part of the infrared energy along the way, so how much you lose depends on how dense they are and how far you are looking, and dense fog can leave you without a useful image.

• Fog. Fog is a cloud of tiny water droplets near the ground, and liquid water absorbs infrared strongly. Light mist usually costs a little contrast. Thick fog can shorten how far you notice a heat source and soften the edges of what you do see.
• Rain. Rain fills the air with droplets and also wets and cools surfaces in the scene, which can flatten the temperature differences a thermal image depends on.
• Smoke. Thermal tends to handle smoke better than the naked eye, but dense smoke still costs detail. Our article Can a Thermal Scope See Through Smoke? goes through it in depth.

Ten night vision overview sums it up well: thermal cameras can see through light fog, rain and smoke “to a certain extent”. Thermal often keeps working when your eyes and a day scope don’t, but no weather is free.

What This Means When You’re Scanning

A thermal device needs open air between its lens and the surface you want to read: no glass, no water and as little cover as you can manage. That holds for a handheld unit from our monokular termowizyjny range and for a thermal riflescope alike.

A few situations come up again and again:

• Scanning from a vehicle, blind or house. Any glass between you and the field blocks the scan. Open the window, or use an opening with no glass in it.
• Clip-ons in front of a day scope. If glass blocks heat, how does a thermal clip-on work in front of a glass day scope? The clip-on’s sensor faces the open air and turns the heat into a picture on its own screen, and the day scope behind it only looks at that picture. Every Taurus clip-on model (PFI-T425, PFI-T435, PFI-T635 and PFI-T650) lists a 1920 × 1080, 0.49-inch OLED screen and 1.0× magnification.
• Wet nights. A sealed housing keeps a device working in the rain, but it doesn’t change what rain does to the image. All four Mile 3 models (PFI-M325, PFI-M335, PFI-M625 and PFI-M625 LRF) list an IP67 protection grade and operating humidity of up to 95%.

FAQ

Can Thermal See Through a Car Windshield?

No. A windshield is glass, so the screen shows the glass’s surface temperature and reflections from inside the car. Lower a side window or step out to scan.

Can Thermal See People Through Walls?

No. A wall blocks the infrared energy from anyone behind it, so you only see the wall’s surface temperature.

Why Do Eyeglasses Look Dark on Thermal?

The lenses block long-wave infrared, so the camera reads the lens surface instead of the warm eyes behind it. The lenses are usually cooler than the skin around them, so in White Hot they tend to look darker than the face.

Can Thermal See Fish Underwater?

No. Thermal reads only the top layer of the water’s surface, so fish below it stay hidden. You will see anything that breaks the surface, such as a swimming animal’s head.

Can Thermal Imaging See Through Fog?

Partly. Light fog usually costs some contrast, while thick fog can shorten how far you notice a heat source or hide it completely. Thermal generally still does better than your eyes in fog.