Testing was carried out to characterize and predict the long-term thermomechanical properties of Thermal Ceramics Min-K 1400TE thermal insulation material, hereafter referred to as Min-K. In particular, the high temperature gradient stress relaxation behavior of Min-K up to 700 degrees C was evaluated under various thermal gradients and a helium atmosphere for test times of up to over two years. Additionally, finite element and mathematical models were formulated to predict the mechanical behavior exhibited by Min-K out to 50,000 hours based on this testing. This paper discusses the design and construction of unique test equipment to carry out this testing, along with the results of the testing and the subsequent modeling.