During its primary mission, IRAC was able to simultaneously operate in four wavelengths: 3.6 μm, 4.5 μm, 5.8 μm, and 8.0 μm. Each infrared detector had dimensions of 256×256 pixels—a significant improvement over previous spaceborne infrared telescopes—and each image taken covered 5.12 square arcminutes of sky with each pixel covering 1.2 arcseconds. The detectors operating at 3.6 μm and 4.5 μm were constructed with indium antimonide (InSb), while the 5.8 μm and 8.0 μm detectors were made of silicon doped with arsenic (Si:As). The telescope's primary and secondary mirrors, along with its supporting structure, were made mostly of beryllium. The telescope was cryogenically cooled to around ; the 3.6 μm and 4.5 μm detectors operated at and the 5.8 μm and 8.0 μm detectors operated at .
