The Mirka WPF PRO 9 in x 11 in Plain P400 Sandpaper Sheet, model 21-101-P400, is a waterproof abrasive sheet for fine sanding and surface prep. This is a sandpaper sheet designed for manual wet sanding and finish refinement. If you are working on paint, primer, lacquer, metal, wood, putty, or composite materials, this sheet is built to keep the cut consistent while helping you get to a cleaner finished surface.

What matters here is not just that it is P400 grit, but what that grit does in real work. Fine grit like this is typically used when you are past heavy material removal and into the stage where surface quality starts to matter more than speed. The scratch pattern is described as highly polishable, which is exactly what you want when sanding between coats, refining primer, or preparing a panel or part for topcoat.

Mirka positions the WPF Pro line as a high-quality waterproof abrasive with a lasting aggressive cut. In practical terms, that means the sheet is made to keep working instead of falling off fast once moisture is involved. It is also described as curl resistant and non-absorbent, which is important for wet sanding because paper that swells, curls, or goes soft gets frustrating fast and makes it harder to keep pressure even across the surface.

The C-weight latex paper backing is there for flexibility. That matters when you are sanding curves, contours, body lines, edges, or repair areas where a stiff sheet can leave uneven contact. A more flexible backing helps the abrasive follow the surface better, especially when used by hand or wrapped around a sanding block.

This Mirka abrasive sheet is suited for manual sanding jobs across several materials, including paints, primers, lacquer, metal, composite materials, putty, and wood. That makes it a practical choice for auto body repair, paint prep, finish sanding, and general shop work where wet sanding is part of the process. Because it is a plain full sheet format, you can use it as-is, fold it, or cut it down to fit the task.

If you are the kind of buyer who cares more about finish quality than flashy packaging, this is the kind of abrasive worth paying attention to. The Mirka WPF PRO 9 in x 11 in Plain P400 Sandpaper Sheet makes the most sense for painters, body techs, refinishers, woodworkers, and serious DIY users who need a reliable wet sanding sheet that holds up, stays manageable in the hand, and leaves a fine surface ready for the next step.

• Is this sandpaper made for wet sanding? Yes. The WPF Pro is a waterproof abrasive specifically suited for manual wet sanding.
• What materials can it be used on? It is suited for paints, primers, lacquer, metal, composite materials, putty, and wood.
• What does P400 grit make it good for? P400 is a fine grit typically used for finish sanding, surface refinement, and prep before final coating or polishing steps.
• Is this a full sheet or a hook and loop disc? This is a plain 9 in x 11 in sheet, not a disc.

Simple Sheet, Serious Finish Work

The Mirka WPF PRO 9 in x 11 in Plain P400 Sandpaper Sheet is a smart buy if you need dependable wet sanding paper that stays usable and leaves a cleaner finish than bargain-bin sheets.

• Who it's for: Painters, body techs, refinishers, woodworkers, and detail-minded DIY users doing fine prep work.
• Why it stands out: Waterproof construction, flexible C-weight latex paper backing, and a polishable fine scratch pattern make it a strong choice for finish-stage sanding.
• Worth knowing: This is a manual full-sheet abrasive, so it is best for hand work or cutting to fit a block, not for random orbital sanding.