Fantasy involving tubed sheets of paper (4-5)

I believe the answer is:

pipe-dream

I'm a little stuck... Click here to teach me more about this clue!

'fantasy' is the definition.
(I know that pipe dream is a type of fantasy)

'tubed sheets of paper' is the wordplay.
'tubed sheets of' becomes 'piped' (I can't justify this - if you can you should give a lot more credence to this answer).
'paper' becomes 'ream' (a ream is an amount of paper).
'piped'+'ream'='PIPE-DREAM'

'involving' acts as a link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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