Orthodontic power chains are replaced at 3 to 4 week intervals due to force decay. Studies on power chains often do not differentiate between thermoplastic (TP) and thermoset (TS) elastomers and, to date, no study has compared between them. We sought to compare over a period of 8 weeks: (1) force decay between TP and TS power chains, (2) force decay between using two different initial forces, (3) force decay between direct chains and chain loops. Our results showed 20% more force decay in the TP power chains compared to the TS ones. Direct chains had more force decay compared to chain loops only in the OrTP power chains. There was no significant difference in force decay between using light and heavy forces. In conclusion, contrary to the interchangeable use of TP and TS power chains in published literature and in clinical practice, this study demonstrates that they perform differently under stress and that a clear distinction should be made.