Speed of development
EASY TO USE
Pre-tested modules and uniformity across modules (color, style, effect, feel)
A LOT OF TOOLS
Mobile-ready, and feel the same as the new Android L interface (Android L and Polymer were designed using the same UX principles of Material Interface)
Polymer is a project sponsored by Google. Polymer is a library of ready-to-use, freely composable web components that you can use to build applications or new web components. Polymer also includes standard polyfill scripts to ensure that the library behaves the same in all modern browsers.