Render Issue: Material: Glass vs Clear Plastic

i am testing clear materials.

i have just noted that a "glass" material on an object took 57secs to render (800x600px) vs 37minutes for the same part in "clear plastic".

i would have imagined that the "clear plastic" has no or limited refractions and would have rendered even faster than the glass.

anyone else find this? any explanation?

i am also using keyshot. it has a material called "window" which uses limited refractions similar to a clear plastic.

as a side note, Keyshot to render the same scene, was about the same render time for the "glass" material in Photoview, maybe a little quicker but not much.

BR

Mitch

SolidworksPhotoview 360