An integrating-sphere system was created to measure optical properties of materials in the infrared range. It accurately measures how much light passes through, reflects off, and gets absorbed by different samples. The system uses a special spectrophotometer to analyze various materials, both opaque and transparent. The measurements are very precise, with uncertainties less than 0.003 over a wide range of wavelengths. The sphere can be adjusted to test samples from different angles. While this system was designed for infrared light, it can be adapted for use with other types of light as well.