Finishing the underside of kitchen wall mounted unit

MDF moisture resistant, can router a decretive edge before painting it if needs be

For finishing the underside of your kitchen wall mounted units, a smooth and paintable material that can be glued in place would be ideal. One suitable option is plywood. It is a versatile and durable material that can be easily cut to size. Choose a high-quality plywood with a smooth surface finish to ensure a professional look. Prior to gluing, ensure the surface is clean and free from any debris or grease. Once the plywood is securely glued in place, you can paint it to match the rest of your kitchen décor. Remember to use appropriate paint and primer for the best results.

As mentioned you could use mdf. Or another option would be to buy some end panels that will be finished already. These can be cut to fit on base of wall units.

You can also use iron on edging tape. It’s the same look as the edge of cabinets then.