Currently we have an issue that IE 11 is showing PBR materials more sharp/shiny compared to other browsers. This seems to be more noticeable for small roughness values.
Here is a small example (sorry i couldn’t use the Playground because it does not support IE):
http://jsfiddle.net/mv7j2094/1/embedded/result,css,html,js
Chrome Screenshot:
IE 11 Screenshot:
Unfortunately this is expected because IE only supports a subset of the webgl features required to correctly render roughness.
We have some fallbacks but we cannot completely overcome the missing feature
Pinging @sebavan as I think it should be possible to control a bit how we generate the textures for IE to get more or less roughness
Unfortunately ie does not support texture lod and it usually is ok-ish as most of the materials are not as homogenous as yours. Unfortunately in your case there is not much we could do as we basically manually blend between 2 textures to fake an accurate fetch of the corresponding roughness.
Thank you. Hopefully our customer will accept this limitation … and hopefully IE is dead soon 
Can’t agree more!