The phrase "a plain sheet" is correct and usable in written English.
It can be used to describe a sheet of paper that is unadorned, without any designs, patterns, or text.
Example: "Please hand me a plain sheet to jot down my notes."
Alternatives: "a blank sheet" or "a simple sheet".
His oath took the form of a handwritten letter on a plain sheet of paper to the Constitutional Council.
It came in a plain brown envelope, and was handwritten on a plain sheet of white A4.
We can be tricked by the orderly appearance of the trellised rows into thinking of the vineyard as pinstripes on a plain sheet.
"The list would be handwritten on a plain sheet of paper — there was no logo, no official stationery," Mr. Mansour said.
Even the discharge papers from the Turkish hospital were carefully prepared -- they are on a plain sheet of paper with no address or telephone number.
The target material needs to be clamped to the magnetron body and for a plain sheet of material, this requires a clamping ring.
A light-colored blank wall works fine as a projection screen, or, if this is not available, you can hang a white (or light-colored) plain sheet with thumbtacks.
Stick pages from an old book onto the plain sheet.
By wrapping his subjects in a plain white sheet rather than the clothing and jewellery we use to conceal ourselves he is asking: "Is this your true self?
Like three of the other present occupants, Jane is still in the hospital gown she died in, but she will be cremated naked, cocooned in a plain white sheet.
Some of the gizmos work (paperless check-in is executed well), while others are a fad too far (iPads loaded with the restaurant wine list, plus reams on grape varieties, might better have been delivered on a plain old sheet of A4).
