Breast implants are made of a flexible silicone rubber shell filled with either sterile saltwater (saline) or silicone gel. Every implant approved for use today shares that same basic silicone outer shell, though the filling inside and the engineering of each layer vary significantly between types. Here’s what goes into each component.
The Outer Shell
Regardless of what’s inside, the outer envelope of virtually all breast implants is made from silicone rubber, specifically a family of compounds called polysiloxanes. The two main types used are polydimethylsiloxane and polydiphenylsiloxane. During manufacturing, these silicone polymers are chemically cross-linked (bonded together into a tight network) and cured into a flexible, durable elastomer. Tiny amounts of amorphous silica are mixed into the shell as a reinforcing filler, similar to how rubber tires use fillers for strength.
Modern shells aren’t a single uniform layer. They typically include a barrier layer sandwiched between the outer and inner surfaces. This barrier is designed to minimize “gel bleed,” the slow diffusion of silicone molecules through the shell wall. One established approach uses a fluorosilicone elastomer for this barrier, a modified silicone that resists the passage of gel fluid. In newer implants like the recently approved Motiva line, the barrier layer uses a separate silicone elastomer formulation and even includes a blue pigment indicator so surgeons can verify the barrier is intact during manufacturing.
A small patch on the back of each implant covers the hole left during production. This patch is bonded with medical-grade silicone adhesive and reinforced with the same barrier material used in the rest of the shell.
Smooth vs. Textured Surfaces
The outside of the shell comes in two finishes: smooth or textured. Smooth shells have a uniform surface. Textured shells have a roughened exterior created through several different methods depending on the manufacturer. The most common technique is the salt-loss method, where grains of salt (in sizes ranging from 150 to 500 micrometers) are pressed into the uncured silicone, then dissolved away after the shell hardens, leaving behind a pattern of tiny pits and ridges. Other manufacturers use gas diffusion, imprinting, or a layer of polyurethane foam bonded to the shell surface.
Texturing was originally developed to help the implant stay in position and reduce the risk of the scar capsule tightening around it. However, certain aggressive texturing patterns have been linked to a rare cancer called breast implant-associated anaplastic large cell lymphoma, leading to recalls of some textured designs.
Saline Implant Filling
Saline implants are filled with sterile isotonic saline, the same concentration of salt water used in IV bags: about 0.9 grams of sodium chloride per 100 milliliters of water. The implant shell is inserted empty and then inflated to the desired volume through a small valve during surgery. This allows the surgeon to fine-tune the size and means the incision can be smaller than with pre-filled silicone gel implants.
If a saline implant ruptures, your body simply absorbs the salt water harmlessly, and the deflation is obvious almost immediately because the breast visibly loses volume. Early saline implant designs experimented with other filling solutions like dextran (a sugar-based fluid), but modern versions use plain saline exclusively.
Silicone Gel Filling
Silicone gel implants are pre-filled at the factory with a medical-grade silicone gel made from polydimethylsiloxane (PDMS) polymers. What makes the gel thick or firm is the degree of cross-linking between those polymer chains. During manufacturing, some of the chemical groups on the polymer chains are swapped out for reactive groups that form two-carbon bridges between neighboring chains. More bridges mean a denser, firmer gel.
This is where the concept of cohesivity comes in. A less cohesive gel behaves more like a thick liquid, flowing and deforming easily. A highly cohesive gel holds its shape, resists gravity, and bounces back when compressed. Manufacturers offer implants across a range of cohesivity levels because the tradeoff is straightforward: firmer gels hold their shape better and cause less visible rippling, but they feel less like natural breast tissue. Softer gels feel more natural but may not maintain upper breast fullness as well over time.
So-called “gummy bear” implants sit at the high end of the cohesivity spectrum. Their gel is cross-linked so densely that if you were to cut one in half, each piece would hold its shape rather than ooze, much like cutting a gummy bear candy. These form-stable implants are particularly useful for anatomically shaped (teardrop) designs, where maintaining a specific contour matters. The tradeoff is that highly cohesive implants can sometimes flip within the pocket, rotating their shaped profile into an unnatural position.
If a modern silicone gel implant ruptures, the cohesive gel tends to stay together inside or near the shell rather than migrating through surrounding tissue. This is a significant improvement over pre-1992 implants, which contained a much runnier gel that could spread more freely after a rupture.
Trace Metals in the Manufacturing Process
Platinum is used as a catalyst to cure both the silicone gel and the elastomer shell. Small amounts remain in the finished implant, typically at parts-per-million levels. A 250-gram implant contains roughly 175 micrograms of platinum. Studies reviewed by the FDA and the Institute of Medicine have consistently found that this residual platinum is in its elemental (zero-valence) state, which has low toxicity, rather than in more reactive chemical forms.
FDA-mandated testing of implants also screens for a wide range of trace elements including titanium, chromium, nickel, copper, zinc, tin, and lead, all at concentrations low enough to meet biocompatibility standards. Small amounts of volatile compounds, including trimethyl silanol and cyclic siloxanes, can also be detected in the shell material.
How Your Body Responds to These Materials
Medical-grade silicone is considered biocompatible, meaning it doesn’t provoke a severe immune reaction in most people. That said, your body does recognize any implant as a foreign object. Within the first few weeks after surgery, the immune system sends inflammatory cells to the area and begins building a thin fibrous capsule of scar tissue around the implant. This capsule formation is a normal, expected response.
In histological studies, the tissue surrounding silicone implants shows a mild to moderate chronic inflammatory reaction with fibroblasts (scar-building cells) and occasional immune cells called macrophages and giant cells. By about 30 days, the tissue typically matures into an organized collagen capsule. In some people, this capsule tightens excessively over months or years, a complication called capsular contracture that can cause firmness, discomfort, or changes in breast shape.
Lightweight and Alternative Implants
A newer category of implant reduces weight by up to 30% compared to standard silicone gel implants of the same size. The B-Lite implant achieves this by embedding hollow borosilicate glass microspheres throughout the silicone gel. These microspheres are each larger than 30 micrometers, surface-treated to bond tightly to the surrounding gel, and chemically inert. Borosilicate glass is the same corrosion-resistant material used in laboratory glassware and certain pharmaceutical applications. The bond between the microspheres and the gel is engineered to be stronger than the cohesive forces within the gel itself, preventing the microspheres from separating or migrating through the shell.
The FDA also recognizes a broader category of “alternative” breast implants, defined as any implant that uses a filler other than saline or silicone gel, or a shell made from something other than silicone rubber. These remain relatively uncommon compared to the two standard types.
What the FDA Requires Manufacturers to Disclose
Every breast implant approved in the United States comes with a Summary of Safety and Effectiveness Data that lists every material in the device. For a typical silicone gel implant, this includes the specific silicone elastomer dispersions used for the shell layers, the barrier layer formulation, the patch adhesive compounds, and the platinum-cured gel filler. Some newer implants also contain a passive RFID microtransponder for identification, made from copper wire, a nickel-zinc ferrite core, acrylate adhesive, and a soda-lime silicate glass casing. These labeling documents are publicly available through the FDA’s online database, so you can look up the exact materials for any specific implant model before surgery.