Fidelis beat me to it, but since I’m here, I thought I’d define them for those who might not be familiar with the distinction. “Materially” sufficient means that Scripture contains, either explicitely or implicitely*, all that has been revealed for salvation. However, it is not “formally” sufficient in that one can interpret this revelation through Scripture alone. It must go in tandem with Sacred Tradition and the Magisterium.
Some of the implicit stuff, such as the Assumption, are very indirect and more implied (than actually stated) by the logical conclusions one might draw from Mary being immaculately concieved. Either way, the material sufficiency emphasizes that nothing in Scripture will contradict what might be more explicitely stated through, say, Sacred Tradition.
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