MDF vs Plywood as building material

My father is installing a pocket door, and he has to narrow the doorway by 1 inch on the pocket side of the pocket door. He has 3/4" oak strips he'd like to use. He was thinking of using 1/4" plywood or 1/4" MDF to make up the difference (it won't be visible as the trim will cover it anyway). I'm wondering if either the MDF or plywood will rot/warp/fall apart over time, and how it should be treated prior to installation.
Thanks
John
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Shims are standard method, adjustable, easier to set the jambs dead plumb.
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On Thu, 27 Jan 2011 07:09:19 -0800 (PST), John

MDF or plywood would both be OK. I think I'd prefer plywood, but I'd like to see MDF glued on if he used it, in case it did try to separate near the edges with a nail or screw going through it. Both are solid enough for final shimming to fit the new jamb and trim.
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