There are curtains in The Sims 4 that are animated, and they use a specific object shader called 'InstancedVertexAnim'. I have noticed an issue with this particular shader in that the specular map (the shininess) and normal map (extra surface detail) do not appear to function as expected.
The curtains lack shininess and are instead completely matte. They have their own unique specular textures, like any other object, but they simply do not work.
For the purposes of conveying information, I created separate versions of a few curtains from Seasons and Get Famous to use a different object shader than that of 'InstancedVertexAnim'. And the difference is noticeable (top image is the original, bottom is my duplicate with a different shader):
Another thing of note here is that the normal map ("trick" to achieve further 3D detail without more polygons) does not appear to be working on curtains using 'InstancedVertexAnim' either, despite them having one. I wasn't able to get a good comparison picture of that, but it can be seen with the same Get Famous curtain right above. The golden "curtain holder" has more of a 3D look to its surface and its carvings when using a different shader than how it is in-game at the moment.
And so, I expect that the 'InstancedVertexAnim' object shader would allow for functioning specular and normal maps.
Tested, and pictures taken, without CC, mods or customized visuals.
