So, what changed this year? First, the transparent switch cover material.

The cover in the 2018 model is semi-opaque, somewhat tacky, and feels like silicone. The new model is clearer and smooth to the touch.

To confirm that the materials are indeed different, we analyzed them using Fourier Transform Infrared (FTIR) spectroscopy. Thanks to Eric Beaton and Cal Poly's Materials Engineering department for their equipment and expertise!

FTIR analysis works by shining infrared light at a material and measuring how much light is absorbed and at what wavelengths. This data acts like a fingerprint that can be used to identify the material.

The differing peaks and valleys on the FTIR spectra for the two samples show us that they are different materials. But what are they?

When comparing these FTIR spectra to that of known polymers, the closest match for the 2018 model is either poly(acetylene) with aromatic urethane side groups, or a type of TPU (which seems more likely). The 2019 model is a match for polyamide (commonly known as nylon).

What this doesn't tell us is, just what problem Apple's engineers tried to solve using this updated material. Send us your ideas!