Materials are Considered Uncountable Nouns

Materials (glass, wood, iron, stone, paper, cloth, wine, coffee, tea &c.) are considered uncountable. But many of these nouns can also denote one particular thing, and then take an article:

Windows are made of glass but Have a glass of wine.
We write on paper but I've got a (news)paper.
Iron is a metal but I use an electric iron.

Some, any, a piece of, a lot of &c., are often used.

• Would you like some coffee?
• I want a piece of wood.

Indefinite Article is Not Used Before Uncountable Nouns

The indefinite article is not used before uncountable nouns.

The following nouns are singular and uncountable in English.

• advice
• information
• news
• baggage
• luggage
• furniture

They are often preceeded by: some, any, a little, a lot of, a piece of &c.

• I'll give you a piece of advice.
• You need some more furniture.
• There isn't any news.

Knowledge is also considered uncountable, but when used in a particular sense takes the article:

• A knowledge of languages is always useful.
• He has a good knowledge of mathematics.

Hair (all the hair on one's head) is considered uncountable, but if we consider each hair separateley, we say: a hair, two hairs &c:

• She has black hair
• The fisherman used a hair to tie the feather to the hook