I) Both the words material and materials can be used when we want to refer to physical objects.
- not enough material for two overcoats.
- a few meters of dress material.
- Stone is a durable material.
- Writing materials such as paper and pens.
- Dress materials.
II) material (legal) = important, essential.
- material evidence
- The judge warned the witness not to hold back material facts.
BUT, when you want to mean information or ideas (non-physical) you must use MATERIAL not MATERIALS.
- I hoped to find material for some articles.
- She is collecting material for a book.
- He wrote a good deal of material himself.
- They researched a lot of background material.