Most materials expand upon heating and contract upon cooling. Some behave inversely, a phenomenon known as negative thermal expansion (NTE). NTE observed in inverse perovskite antiferromagnets Mn3AN had remained unexplained for the past 40 years. However, a recent study by scientists successfully provided a theoretical explanation to this mechanism. When turn into practical use, this could help developers build more durable and heat-resistant small machine parts — found commonly in optical, measuring and other devices.