Find the Right Mix.
"Sadly there’s no magic cotton to elastane ratio, but I definitely think the weight of the denim makes a huge difference. Depending on the style you’re picking, heavier-weight denims are best because they typically are a bit more flattering (they hold you in) and they’re less likely to be sheer. I’m a big fan of 11 oz. denims in either a superstretch denim for skinny jeans, or a 98 percent cotton / two percent elastane fabric content for flares, straight-legs, shorts, and boyfriend styles."