Some implants had internal dividers to keep the gel from sagging into the central part of the implant. Seal patches were used to close up any holes or slits left by manufacturers or the valve entrance to an expander, and are still used for manufacturing today's seamless implants.

By the late 1960s, Dow's shells had become less thick and were seamless. And in 1968, Heyer Schulte Corporation became the first domestic manufacturer of saline-filled implants. Early saline implants were fragile and heavy, with audible “sloshing,” and there was a very high deflation rate of up to 76%, probably because of the high-temperature vulcanizing process used to “cure ” or strengthen the contents.

The original thick-shell models were replaced in the 1970s and early 1980s by implants with thin shells. But these had a greater tendency to rupture and deflate. These “second-generation” implants were generally smooth surfaced and had high contracture and gel-fluid seepage rates. More flexible gels were introduced by various companies from 1972 to 1975, and thinner elastomer shells were introduced starting in 1972.

Another development in the 1970s was a polyurethane foam coating on the implant shell. This coating appeared to reduce contracture and was popular; an estimated 110,000 women or more received this type of implant before it was discontinued in 1991. The polyurethane coating appeared to diminish capsular contracture by causing an inflammatory reaction. This reaction discouraged formation of fibrous tissue around the capsule. But the polyurethane coating started disintegrating almost immediately, so that what eventually remained was a mostly smooth implant surrounded by a capsule containing foam fragments. Pain, fluid accumulation, and infection were reported. The foam fragments were one reason a polyurethane-coated implant was difficult to