Machine Design – May 2019

ePTFE and Athletic Shoes

the upper construction, essentially

becoming “invisible” so the wearer

doesn’t know it’s there, thus the name.

Bu Invisible Fit’s 3D Fit footwear’s

major benefit is that it uses a stretch-

ier version of ePTFE. A current trend

in athletic (and urban) footwear is to

make shoes with flexible knit or woven

uppers. In the past, you could not pair

a stiffer ePTFE membrane with these

kinds of stretchy materials. With the

three-layer construction, and a modi-

fied ePTFE, the Invisible Fit is uni-

formly stretchy.

Invisible Fit also decreases drying

times because construction places the

membrane more toward the outside of

the shoe’s upper. This means it keeps

water off of more of the shoe than does

a traditional bootie construction. So

fewer materials need to dry out. Dry-

ing time is reduced whether the shoes

are left on or taken off, but shoemakers

usually define drying times to mean a

process done with the shoes off. Invis-

ible Fit makes for a lighter shoe because

less membrane and seam tape is needed

than for bootie construction.

Although W.L. Gore is a major player in ePTFE fabrics and materials for shoes, it does not

make any themselves. It sells its products to OEMs such as Adidas for its Terrex shoes,

Salmon for its Mesh shoes, and Under Armour for its HOVR Phantom shoes.

Under a microscope, the many pores in it are easy to see. Engineers can tailor the size of the

pores, while ePTFE is made so they are too small to let water molecules in, but large enough

to air molecules pass through.

40 MAY 2019 MACHINE DESIGN