Product review (3 stars): Aprilaire A12 WaterPad
This item is intended as a replacement water pad for a humidifier system.  Its packaging lists it as compatible with:
  Aprilaire 112, 136, 224, 440, 445, 445A, 448
  Chippewa 224, 225, 226
  Walton 600, 620, 660

I ordered this item from Todays Concept.  The item graphic at the time showed an A12W Aprilaire replacement waterpad box.  And the title for the item at the time was "RPS #A12W Aprilaire112 Water Pad" however the item received was a regular A12, not the A12W. The item image has since been updated to show a graphic of the waterpad itself, not the packaging. But the item title still specifies "#A12W" at the time of this review.

Also, the item description at the time of review is a bit sketchy, including "features" unrelated to a replacement water pad, including:
  1-DuraGuard antimicrobial vinyl with a molded wood core
  2-Stylish designs complement your bath dcor
  3-Fits all manufacturer's standard round bowls

The item received (#A12) is actually made of layers of expanded metal (see [...]) coated with a white substance, possibly vinyl or teflon (difficult to say).  The difference with an A12W is that an A12W is often made of expanded plastic and coated with an absorptive material such as paper fiber or cloth fiber.  The absorptive material helps to distribute the water and gives it more surface area from which to evaporate, also it helps minimize wasted water.

Be aware, unless they have changed inventory, you may be receiving an A12 rather than an A12W.