Panels go on the sides of cabinets, and cover up your exposed IKEA cabinet boxes. Adding panels is a design decision. Most folks opt out of side panels only when they are doing a waterfall countertop, or have a Godmorgon unit (adding panels to a Godmorgon means you'll need a custom countertop).
On the left is a Godmorgon unit with Douglas Fir fronts and no side panels, exposing the white IKEA cabinet box. On the right is an upper cabinet with a walnut panel installed on the side of the cabinet to match the walnut shaker cabinet face.
Fillers fill in spaces between your cabinet box and the wall. IKEA recommends a minimum of 2" gap. They're a great way to close off small spaces that would be dust collectors, and to visually extend your cabinets to the wall.
This Godmorgon has a side panel on the left side, and a filler piece installed and scribed to fit the wall exactly on the right side.
Deco strips are installed on your upper cabinets. They can be installed on the bottom to hide your under-cabinet lighting system, or on the top to frame your cabinet or visually extend it to the ceiling. Paired with panels, deco strips can essentially frame your cabinets. We offer two deco strip options - a flat deco strip, and a miter fold light valence.
On the left, a miter fold piece hides under-cabinet lighting. On the right, a miter fold piece is installed on top of the cabinet. The side panel and the top trim piece meet the ceiling. An additional miter fold light valence has been added below to complete the frame.