My swim cap is tighter-fitting; my goggles are lighter-weight; and my swimsuit is constructed of chlorine-resistant polyester.
But aside from that, not much has changed from fifty years ago, when South End Rowing Club members waded into Aquatic Park cove wearing this:
I’d argue that the only truly essential item is the goggles… but this is a family-friendly site.
Marathon swimming resists technology more than most sports, thanks to strict guidelines on swimwear enforced in the English Channel (our Everest) - guidelines which are widely emulated around the world. Indeed it’s a point of pride among many marathon swimmers, who value the connection with our sport’s pioneers. A level playing field across decades.
I’d even call it an aesthetic: Suit, cap, goggles. That’s all we really need. Man, woman, and the sea. There is equipment that would make it easier, but we actively reject it. Our sport is tough, and we like it that way.