such stuff

In William Shakespeare's Tempest, Act IV, Prospero says,

You do look, my son, in a moved sort,
As if you were dismay'd: be cheerful, sir.
Our revels now are ended. These our actors,
As I foretold you, were all spirits and
Are melted into air, into thin air:
And, like the baseless fabric of this vision,
The cloud-capp'd towers, the gorgeous palaces,
The solemn temples, the great globe itself,
Yea all which it inherit, shall dissolve
And, like this insubstantial pageant faded,
Leave not a rack behind. We are such stuff
As dreams are made on, and our little life
Is rounded with a sleep. Sir, I am vex'd;
Bear with my weakness; my, brain is troubled:
Be not disturb'd with my infirmity:
If you be pleased, retire into my cell
And there repose: a turn or two I'll walk,
To still my beating mind.