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.