Based on the provided search results, there is insufficient information to offer a detailed solution. One source is a generic website footer, and the other is a link to a discussion forum without the content of the discussion itself. Therefore, the following answer is based on general professional knowledge for fixing sofa back cushions.
There are several effective methods for restoring sagging or misshapen sofa back cushions, depending on whether they are removable or attached and the type of filling they contain.
For removable cushions that have simply become compressed, the first step is to fluff them vigorously. Remove the cushions from the sofa and pat or punch them firmly on all sides to help redistribute the inner filling. If possible, rotating the cushions to different positions on the sofa can also promote more even wear over time.
If fluffing is not sufficient, the cushions likely need additional filling. Most have a zipper that allows you to access the inner insert. You can purchase polyester fiberfill (such as Poly-fil), foam clusters, or a down and feather blend from a fabric or craft store. Unzip the cushion cover, and if there is a separate inner liner, open that as well. Add handfuls of the new filling, working it deep into the cushion and focusing on the most compressed areas to restore its shape and firmness.
For cushions that are severely flattened or lumpy, you may need to completely replace the filling. Remove all the old material and insert a new foam core, which you can cut to size, or completely restuff the cushion liner with fresh fiberfill. Wrapping a foam core with a layer of quilt batting before inserting it can create a fuller, more rounded, and professional look.
If the back cushions are attached to the sofa frame, the process is more complex. You will typically need to find a hidden seam, often along the bottom or back edge of the cushion. Carefully open this seam with a seam ripper, add the necessary filling to plump it up, and then hand-sew the seam closed using a strong upholstery thread and a curved needle for best results.
