From Bra Maker's Supply:
The fabric is strong and supportive and is a reversible fabric (shiny finish on one side – matte finish on the other). You choose which side to use, according to the look you desire. Duoplex is a low-stretch stable knit made from 100% polyester, and it is the fabric included in our bra kits and the one recommended in the Craftsy class Sewing Bras: Construction and Fit.
Duoplex is 58-60″ (147-150 cm) wide with very little mechanical give (5-7%) in the lengthwise direction.
Duoplex is available in White, Ivory, Yellow, Orange, Peach, Pink, Fuchsia, Red, Black Cherry, Lilac, Purple, Bluebird Blue, Turquoise, Navy Blue, Teal, Forest Green, Beige, Light Copper, Chocolate, Platinum, and Black.
Finish: reversible – shiny face, matte back
Content: 100% polyester
Uses: bra cups