Unique Shaker Ball Mixes Quicker and More Thoroughly Than Standard Shakers Plastic Instead of Metal BPA-Free Dishwasher Safe (Top Rack) NOW Sports Thunderball Shaker Cup powers through thick protein powders and shakes, blending quicker and more thoroughly than standard shaker balls. Unlike a metal shaker ball, our plastic Thunderball floats, so you won’t have to worry about the ball crashing back into the cap when you’re chugging your favorite workout beverage. BPA-free and top rack dishwasher safe, NOW Sports Thunderball Shaker Cups make manual blending a breeze.