What is the most important factor that affects powder and propellant stability?

The stability of powder and propellants is significantly influenced by temperature. Excessive heat can lead to degradation of the chemical compounds within the propellant, causing a change in their burn rate and overall performance. High temperatures may also accelerate chemical reactions that could lead to unintended combustion or unstable conditions.

On the other hand, while humidity can affect certain materials and their performance, it is not as critical as temperature in terms of overall stability. Pressure fluctuations can impact the behavior of gases produced during combustion but do not directly affect the intrinsic stability of the propellant itself. Light exposure can degrade some materials, but it is less impactful compared to temperature effects. Thus, managing temperature is crucial for ensuring the longevity and safe use of propellants.