One of the mainstays of mid-century modern design is upholstered seating with an ultra thin profile, often offering only thin slab cushions resting on a minimal frame. To achieve this, bulky conventional spring cages and other foundational support materials were replaced with elastic rubber webbing. Made by Pirelli, these straps were essentially giant rubber bands with layers of reinforcing fibers to give firm but flexible support. You see these used commonly in loose cushion Danish furniture and office furniture like these Allsteel chairs.
It was a fine idea except for one little detail—natural rubber only has a lifespan of about 20 years. At 30 years the straps soften, lose elasticity and sag. At 40 years they petrify completely and shatter when flexed. You’ve probably experienced this if you’ve ever sat on a vintage chair or sofa and fell uncomfortably far into it (or fell completely through the bottom). The blue chairs above were no exception.
Underneath the straps were stretched far out of shape and were hard and brittle causing the seats to sag. They needed to be replaced, and fortunately it isn’t a tough job at all. I’ll show you how.
First and foremost, you’ll need the right supplies and tools. Although Pirelli webbing is still available, it is expensive and supply is limited. Plus it will be prone to the same deterioration over time. An alternative is woven elastic webbing. I bought a 1,000 foot roll from a boat supply company online (I have a lot of projects that need this stuff), but you can get it from any upholstery supply store by the foot. Be sure to buy the right width (2 inch is the most common) and the type made for seats rather than the stretchier type made for seat backs. Note that jute webbing may be easier to find locally, but it is not the same thing and it will not work. Some furniture will need webbing clips that allow the straps to fit into slots, other pieces will simply have the strapping tacked to the frame. If you need clips, you’ll also need a bench vise or a good pair of vise grips.
My chairs used clips that fit into slots in the steel chair frame. Although I had hoped to replace the straps entirely from the underside of the chair, I discovered there was not enough space to finagle the clips into their slots with the upholstery in place. After cutting off all of the old strapping (do this outside, the rubber disintegrates into a fine powder that gets EVERYWHERE) I also removed the little clips that hold the upholstery in place and carefully removed the vinyl and foam to expose the chair frame. On loose cushion furniture you’ll have easier access as the strapping usually isn’t concealed.
Then I was ready to cut the straps. The most important thing here is not to cut the straps too long or too short. If they’re too long, there won’t be enough support and the seat will sag. If they’re too short, you won’t be able to stretch them all the way across the frame. To get the length right, I attached a clip to one end of the webbing and inserted it into the frame. Then I stretched the elastic webbing as taut as I possibly could and marked where it touched the opposite slot. I cut the webbing at the mark, attached the other clip and then stretched it and snapped it into place. To attach the clips, simply slide it over the end of the webbing and use a vise or vise grips to close the clip so that the teeth grip the webbing. Once complete, I replaced the upholstery and upholstery clips.
The difference is night and day. About an hour of work turned two saggy and completely un-sittable chairs into sleek and comfortable ones without any reupholstery. On wood framed pieces with concealed strapping it might take a little reverse engineering to figure out how to best access the webbing, but the principle is the same. So next time you find a saggy sofa, buy with confidence knowing you can easily shore it up yourself.