If Shatner's toupee could talk and it was asked to pick one moment where it had exceeded all expectations and risen far above and beyond the call of duty, then it would likely select the underwater scenes in the 1986 movie Star Trek IV: The Voyage Home.
More than twenty years on, it is difficult to put into words the impact that Shatner's brief underwater scenes (near the end of the film) had on the world. Three years later, the Berlin Wall was gone and the Soviet Union was nearing collapse.
But just why was this brief scene where Captain Kirk heroically frees a pair of Humpback whales from a sinking Klingon ship such an earth-shattering toupee tour de force? Quite simply, because it caused even the most ardent toupologists to momentarily ask the unthinkable: "Could we have been wrong? That hair looks pretty real."
Just as with many magic tricks, the truth is surprisingly uncomplicated. Firstly, let's not forget that Hollywood, particularly before the days of CGI, had special-effects magicians who could make you believe almost anything you saw was real. Secondly, a toupee you can swim in is actually nothing new at all, especially if you have the magic of Hollywood to help you.
Anyway, Let's go step by step.
Is it really Bill Shatner? Except for one over-the-shoulder-shot where Kirk opens the escape hatch, it is indeed all Shatner underwater (he always loves doing his own stunts wherever possible).
Is it a hairpiece or is it really Shatner's hair? It is definitely a hairpiece; Shats' hair didn't magically grow back, no matter what potion he might have tried. And, if the hair was real, then what the hell were Shatner's hairstylists thinking during so many projects the actor had worked on during the 1970s? Were they trying to make his real hair look fake?
Can we see some bald patches during the swimming? No bald patches are visible since Shatner was completely bald at the top of his head by this time so everything at the top is a full toup. If you photographed a fully-haired person swimming underwater, then you would see the scalp beneath where the hair happens to part as the person swims, because human hair, no matter how thick, does not cover every square millimeter of the head. You see exactly the same effect with Shats, but in his case, the "scalp" beneath an exposed parting is actually the very thin base of the hairpiece to which the artificial hair is attached. Making a toupee base look like a real scalp is really the only way to do it (why would it be blue or red, after all?) and again, it is really a piece of cake for any Hollywood movie hairstylist.
The other question is how the hairpiece was bonded to the scalp in such a convincing and seemingly durable way. Hairpieces in which the wearer can undertake activities such as swimming are actually nothing new. Just watch a James Bond film with Sean Connery or Roger Moore for proof of that. The water tends to ruin them after a while, but for a few shots in a movie - no problem at all. Let's not forget that underwater, the camera tends to see far less detail than it would above-ground and we really don't see that much detail during Shatner's outing, despite a few closeups. As for the fastening, we don't know whether Shats ever had surgery on his scalp to aid hairpiece attachment. The website hairloss.co.uk notes that:
"There can be many benefits to having a permanent wig or toupee, including the decreased risk of the hairpiece falling off during activities and causing embarrassment. With many permanently placed wigs you can swim and take showers without this concern. However, one of the negatives of this is that the wig or toupee can become damaged or faded over time due to chlorine exposure, sun exposure, or repetitive washing. Another downfall of permanent placement wigs is that the application process can be somewhat painful, and in rare cases lead to infections on the scalp or in the hair follicle.
"In order to combat this side effect some wigs are held in place permanently by wire loops that are stitched into the scalp. Others can be permanently attached through a process called 'tunnel grafting'. In this method pieces of skin are cut out and make living loops for the wig. In either case however, cleanliness of the area can become an issue, and some pain or infection can occur. If a permanent type of wig or toupee does not sound right for you, you can look into purchasing its temporary counterpart."