Imagine you have a 1 meter rod of aluminum, hanging vertically. You determine the amount of cooling required to decrease its length by 10 parts per million (10 micro-strain). You then bring it back to room temperature. You hang weights from it and determine the amount of weight required to increase its length by 10 parts per million. Now, you apply the temperature and weight together and see the overall change in length. I used 10 ppm since those are realistic numbers, but imagine if it was 10%. If a material increases by 10%, that is multiplying by 1.1, and if it decreases by 10%, that multiplies by 0.9. If you then do both, you multiply by 1.1 X 0.9 which is 0.99. What appears to be a symmetric process (increasing and decreasing by 10%) is not, since the end result is a reduction of 1%. Is this multiplicative effect how real materials work (is the cold weighted rod shorter than the original), or is it additive such that they perfectly cancel? I assume strains are strains regardless if they are caused by tension, thermal, piezoelectric, or any other effects. This may be misguided.