A jellyfish-proof mask was the protective gear worn by endurance swimmer Diana Nyad in her fifth attempt to realize the Cuba-to-Florida swim in 35 years, CNN reported Tuesday.

Although the 64-year-old swimmer had a team helping her to clear the path and watch out for jellyfish and sharks, Diana's jellyfish-proof mask was considered as the "key difference-maker."

In her previous attempts, Diana cut short in finishing the route because of the venomous sting from deadly box jellyfishes that are common to tropical waters. The protective gear, which she wore only on Saturday because of its complex and cumbersome form, helped her make it through.

"I was grateful for it. I knew I wasn't going to be stung at all. I felt 100 percent prepared for the jellyfish," Diana said after her record swim.

However, CNN reported that due to the design and complex form of the jellyfish-proof mask, Nyad swallowed "tremendous volumes" of seawater from Saturday night and early Sunday, leading her to vomit several times. The endurance swimmer then got dehydrated and demoralized during her swim.

"That night was hell on Earth, it really was," Diana said.

In her website earlier, Nyad shared her thoughts on the protective gear saying, "Literally the only square inch exposed of my entire body was the lips. We just couldn't design a way to protect the mouth and still breathe while swimming."

Fortunately, Nyad did not wear the jellyfish-mask during the crossing after the jellyfish had dispersed Sunday afternoon.

"As difficult as the swimming was, I was not stung once," Nyad said after completing the swim on Monday afternoon. "Those deadly tentacles could not penetrate."

According to the National Science Foundation, box jellyfish is considered one of the most deadly jellyfish in the world because of its paralyzing toxins that attach the skin, the heart, and the nervous system. In the Philippines alone, 20 out of 40 people die from the sting of this jellyfish.