The Egyptians used what are today known as Hieroglyphs while the Sumerians didn't use this kind of language. The Sumerians were one of the first civilizations that actually developed written language which is quite amazing when you think about it.
They wrote in a system that is today known as cuneiform. What is most interesting about their language system is that they wrote down different information on clay tablets which were then further processed with heat in order to make the markings last.
Egyptians on the other hand wrote on Papyrus which was much lighter compared to clay tablets. This, together with the fact that Hieroglyphs were a completely different language system, enabled them to store much more information than the Sumerians :)