When looking to go with a modern look to your bathroom, you can bet that there are many ways to achieve the look.
With so many brands and designs the possiblitites are limitless.
Croscill, the leading brand in shower curtains has a variety types, including but not limited to:
Fabric Shower Curtains:

Double Swag Shower curtains: a more traditional look, may also need a double shower curtain rod.
Vinyl Shower Curtains: Easy to clean, come in variety of designs

Hookless Shower Curtain: most sophisticated look.

Once you find the type of shower curtain you need, then you can begin to find the style you like. For a modern look, striped, circled, and geometric designs will compliment your contemporary feel. Also, sticking with monochromatic color schemes can help modernize your outdated bathroom.
