Penile implants to treat erection problems (erectile dysfunction) are either semirigid (noninflatable) or inflatable cylinders that replace the spongy tissue (corpora cavernosum) inside the penis that fills with blood during an erection. The implants come in a variety of diameters and lengths.
Noninflatable (or semirigid) implants are always firm. They can be bent into different positions (outward to have sex and back toward the body to conceal under clothing).
There are two kinds of inflatable implants. Both have cylinders in the shaft of the penis, a reservoir that holds salt water, and a pump to move the salt water from the reservoir to the cylinders. You create an erection by pumping salt water out of the reservoir and into the cylinders. The release valve on the pump drains the salt water out of the cylinders and back into the reservoir.