The biggest problem with a spring unit, or sometimes referred to as a marshall unit, is not so much the spring itself, but is the 1" or so thick foam that encases the spring unit. This 1" foam that covers the unit on top/bottom is what breaks down first, as its usually not of a high density type foam. This foam on both sides equal to 2" of seating support that once it breaks down and along with the normal softening of the polyester fiber or down/fiber blend wrap, makes the spring cushion a less durable cushion compared to a high density HR foam cushion. If the spring unit is made from a larger stiffer wire, with either a very high density foam topper or a high density polyester pad then the spring unit will outlast a HR foam of same thickness.

Yes there are multiple places. Search “spring down cushions” . Rogers and Brothers, Charles Stewart, etc might be less expensive than local because they make so many and usually for hotels, museums, stores, and private folks. But it’s worth checking around town and make sure you look at the two mentioned (but look yourself) and then look at the Upholstery ones at the end to see the proper way to make these. Always call and ask questions. Did you keep your original springs or did you toss them, they could have been retied and used. Really good spring down ie springs and goose down or if too expensive or allergy issues, many use 4-5 layers of really thick cotton batting over the already wrapped springs and ticking or heavy cotton over the assembly before covers makes for long lasting, resilient seating which can have new decorative covers made for decades and decades. Some use high quality foam wrapped over spring assembly, then cotton and ticking. I just find regular foam breaks down though the springs do help. I have never heard of hand tied hand wrapped springs flattening out unless not tied right to begin. If you want that cushy, sink in type then maybe use high quality pure latex at least 4” thick, covered by 4-5 layers of cotton batting put in both directions thus 8 layers and sewn then a layer of Dacron sewn down to hold it firmly in place. Ask one of these large companies mentioned above what’s best to use for a more cushy feel. A large hook needle helps whip stitched/lock. After that I like to put a zippered ticking or heavy cotton cover on. And then make the final covers. Use a vacuum to drawn cushion assembly down to fit in the cover and might need cotton to fill corners out. See J.A. Milton and Buckminister Upholstery in how tos. I wash the fabric first (at least the under covers) as I know at some point I might want to remove and wash - best to get the shrinkage over and done. Same with decorative covers unless I know I will get them dry cleaned — the best way to keep looking new and with some fabrics your only choice. Check that when buying fabric as to stain resistance, required cleaning, etc. I like to buy a separate couple of yards from that I plan to use and wash and dry it to see how it does. One yard I wash and thrown in dryer and the other wash and hang to dry and iron or steam. I do it this way in case I need to return the larger piece, if they will let you return a whole piece as it was sold. Ask before it gets cut and you leave with it. I got rid of my old thick and heavy latex mattress with heavy cotton and striped ticking on it that I had for about 30 years and was given to someone who used it in their cabin for several years until a bear got in and torn it up. Maybe he was trying to carry it home and it was too heavy. I was stupid to get rid of it — never slept right on all these 18-20” mattresses, weird foams and smells. I finally have pure latex/pure cotton and wool now, no chemicals, won’t go back. (Avocado). The only thing I don’t like is no flipping over, do have to rotate often though. I think rotating and flipping keeps it in shape the best but they make more and more where you can’t flip. Hope this helps others as I realize this is a pretty old post.

Kimdh, If the band= border / boxing finishes 4" then your cushion core should finish 4 1/2", thats without the down wrap or down envelope as what its normally called. The cushion core will consist of the spring unit and the foam that its placed into, as their should be foam around the sides as well as the top and bottom. You want to be able to flip the cushion. Normally it will have 1" foam on top and bottom but I prefer to put a very dense pad over the spring unit, normally referred to deck pad, its about 1/4" to 3/8" thick and available at many upholstery supply outlets. This isolates the wire from the foam toppers and keep the springs from cutting through the foam. If you could increase the border finished size to 5" it would work better. As if you put in a too thick of a cushion core in your cushion, first it will be hard to fill and the cushion will suck in at the sides and not fit. Actually the cushion should be cut with a swell: meaning that the fabric is so that the center of the cushion is wider than the corners, so that the cover compensates for the extra thickness in the core, allows the welts to be straight and not blown out. I seen this a number of times with manufacturers who don't know how to develop a cushion correctly.

I recently bought a couch rom Ralph Lauren and it came with ultra blend couch cushions. The cushions started to flatten. I did;t know a whole lot about couch cushions. they are willing to replace the cushions for more firm cushions, however they do not have the two most firm cushions to sit on in the store for me to try. These are the two cushions I have to choose from. the representative at Ralph Lauren is saying that the Luxury foam fusion is the most firm and the Springdown is 2nd most firm. Please anyone give me advice on what you would pick. I am attaching the discription of both cushions. Please help me decided what to get. I would like something very firm, this couch needs to last us a while, and it is our main couch, so lots of people will be sitting on it, I am looking for most firm couch. However, wouldn't an all foam couch be not so firm and a spiring couch be more firm. Anyway please see attached photos for description.