Many applications rely on the ultra-precise timing of optical signals through fiber, such as fiber interferometers, large telescope arrays, in phase arrayed antennae, optical metrology, and precision navigation and tracking. Environmental changes, specifically those caused by temperature fluctuations, lead to variations in the propagation delay of optical signals and thereby decrease the accuracy of the system’s timing. The cause of these variations in delay is the change in the glass properties of the optical fiber with temperature. Both the refractive index of the glass and the length of the fiber are dependent on the ambient temperature. Traditional optical fiber suffers from a delay sensitivity of 39 ps/km/K. We are reducing the temperature sensitivity of the fiber delay through the application of a novel design of optical fiber, Anti-Resonant Hollow Core Fiber. The major improvement in the thermal sensitivity of this fiber comes from the fact that the light is guided in an air core, with very little overlap into the glass structure. This drastically reduces the impact that the thermally sensitive glass properties have on the propagation time of the optical signal. Additionally, hollow core fiber is inherently radiation insensitive, due to the light guidance in air, making it suitable for space applications.