The difference in absorbed power for the SiN strings and the SRN strings is not surprising and probably just an effect of the two different materials exhibiting different absorbances of the 633 nm laser light. A further comparison of the two sets of measurements suggests that SRN has a higher thermal conductivity than SiN, as the relative frequency shifts for short SRN strings trend towards values below the linear fit of the data set, indicating dissipation of heat.