Because of the quick-drying nature of acrylic paints, they can't be left on an open palette for long and the "stay-wet" system is an admirable solution to the problem of working with what is, after all, what is considered to be the main strength of this medium.
The stay-wet palette consists of a plastic tray with a layer of absorbent paper. This is then soaked and the semi-permeable "membrane" paper laid on top. Acrylic paint can be placed on the membrane and, with the plastic lid covering the tray, the paint stays moist for ages.
I was a bit dubious about its effectiveness at first, since the tray is rather large and has additional spaces for paint tubes and brushes built in. Rather than being hand-held, it will have to be left on a surface beside your artwork, but this should be no big drama since workers in acrylics will need something to sit a lot of water jars on anyway. If you find that you've added too much water at first, simply leave the plastic lid off for 20-30 minutes to allow some evaporation.
One thing to note: the net price for the reservoir & membrane set may seem to be good value, but check the postage & packing before placing your order.
Brilliant if you use acrylic paint, mixed paint stays wet ready for your next painting section, though Im in Spain so it does dry out a little in the heat of the summer (july /August) so I I just give it a quick spray with water, bu cant imagine not having it, as it does save wasted paint, and I paint for a living.
Rowney is quality and therefore it's the best product if you take your painting serious. These refills go with my wet pallet perfectly and save me a fortune due to no wasted paint when I use acrylics.
Just a point, never get a refill that is too small for your pallet, it really needs to go to the edges otherwise you may end up with to much water overflowing into your paints causing them to bleed into each other.