When people are talking about a single paper, they usually use the words "piece of" or "sheet of" before the word "paper."
（「sheet of」とは日本語で「一枚」の「枚」という）
When a piece of paper is not very thick, we refer to it as a "thin" piece of paper--or a "thin" sheet of paper.
e.g.
The present was wrapped in a thin piece of paper.
He always liked painting on thin sheets of paper.
紙一枚について話しているときは、"paper"という単語の前に"piece of"あるいは"sheet of"という単語を使います。
（「sheet of」とは日本語で「一枚」の「枚」です）
紙があまり厚くない場合は、a "thin" piece of paperまたは a "thin" sheet of paperと言います。
【例文】
The present was wrapped in a thin piece of paper.（プレゼントは薄い紙に包まれていた）
He always liked painting on thin sheets of paper.（彼はいつも薄い紙に絵を描くのが好きだった）
▪ Thin paper
Thin means it has very little thickness.
▪ Slim paper
Slim is another word for thin.
Example sentences:
a. Do you have any thin paper?
b. I enjoy writing on slim/thin paper.
▪ Thin paper(薄い紙)
Thinはとても薄い厚さであることを意味します。
▪ Slim paper（薄い紙）
Slimはthinの別の言い方です。
例文
a. Do you have any thin paper?
（ 薄い紙を持っていますか？）
b. I enjoy writing on slim/thin paper.
（私は薄い紙に書くことが好きです。）
When talking about a unit of paper we usually say a piece or a sheet of paper. Therefore to describe thin paper, we would say :-
1. A thin piece of paper.
2. A thin sheet of paper.
1枚の紙の事を言う場合は ”a piece of papre" か ” a sheet of paper.”と言うので、薄い紙と言う時は以下の様に言えます。
1. A thin piece of paper.
（１欠片の薄い紙）
2. A thin sheet of paper.
（１枚の薄い紙）
Explanation: The adjective THIN describes something that is narrower than average. If it is very thin, you can use VERY or VERY VERY, or the superlative, the thinnest, or the adverb REMARKABLY.
Example sentence:
'Henry is remarkably good at badmington.'
説明: 形容詞の "THIN "は平均より細長いことを示す言葉です。とても薄い場合はVERY やVERY VERYあるいは、 "superlative"（この上ない）, "the thinnest"（最も薄い）,副詞の "REMARKABLY"（特筆して）.と言うことができます。
例文:
'Henry is remarkably good at badmington.'
（ヘンリーはとてもバドミントンが上手です。）
"Thin," would be the word to use to describe the thinness or thickness of a certain thing. We can also use the words, "a piece of paper," or, "a sheet of paper," to have the same meaning, or we can simple say, "a thin paper," without using either one of these words.
例：
fine paper (or heavy ) is based on its GSM, (Technical huh?)
GSM is an acronym for 'Grams per Square Meter'.
Quite simply, it allows print buyers and print suppliers to know exactly the quality of
paper being ordered.
The LOWER the GSM number, the LIGHTER the paper
& VIce Versa;-D
アメリカ合衆国 
南アフリカ 
カナダ 
イギリス 
