The commercial for Furniture Fix hypes a system of 18-inch long plastic panels that interlock to accommodate various upholstered seat sizes.
It takes one box of six panels for a typical upholstered chair and two or more boxes for a sofa, depending on the sofa length. Each box sells for $14.99.
Since Furniture Fix first came out several years go, the makers have added plastic end caps to give extra panel support. In our test, we found the end caps difficult to attach to the panels. But the interconnecting panels do slide together easily.
Once the panels are connected, remove the cushions and lay the panels them across the sofa bottom. You're supposed to alternate the panel positions, one up, one down, to distribute the support.
To our surprise, it worked. The college house mates who tested Furniture Fix on their 20 year old sofa said they could definitely feel more support and the sofa no longer sagged when they sat down. The were so impressed, they're thinking about buying it so solve their saggy situation.
On a scale of one to four, they give Furniture Fix gets a solid three. They do wonder, however, how well the thin pliable plastic panels hold up over time.