Greetings,
There was a short part of my left where I specialized in injection molding.
Today I am holding a plastic cup, much like the image below, that has bubbles in it.
None of the bubbles are surface connected nor are they very close to the surface (I've tried to pierce them with a knife).

I cant wrap my head around how this is made? Are they preloading the mold with something?
I thought maybe they are not bubbles but rather solid spheres... but I don't think so. Up close, their shape is inconsistent and irregular, like you would expect to see with bubbles.

I'm fairly sure the cup is acrylic.

Anyone know how they make cups like this?

VS

• http://files.engineering.com/getfile.aspx?folder=26035bf6-fcd5-4cd8-858b-ee