How many kinds of endoplasmic reticulum are there?

There are two kinds of Endoplasmic Reticulum:

Rough Endoplasmic Reticulum (Rough ER): The surface of rough endoplasmic reticulum is covered with spherical organelles called ribosomes. Rough endoplasmic reticulum is involved with protein synthesis.

Smooth Endoplasmic Reticulum (Smooth ER): This type of endoplasmic reticulum is involved with lipid synthesis and detoxification of toxic matters.