Opposite of Paper?

So what do you think is the opposite of paper?

After this question came up in a family discussion it lead to some deeper thinking. Opposites are often quite obvious: Dark – Light; High – Low; Fat – Thin; Sad – Happy.

It seems that with paper for example you can look at various properties and draw different conclusions.

• Paper is white – usually but not always. Coal could be a candidate as it is black.
• Paper can be written on. Water can not be written on.
• Paper can be torn easily. Steel can not be torn.
• Paper is highly flammable. Fire could therefor be considered an opposite.
• Paper is a material. A thought or a feeling is not.

The list could go on – but you get the drift.

Let me know if you have a perfect answer…