Some of the main features of Zip for WPF and Silverlight that you may find useful include the following:     

• Standard-based
  Load data from existing zip files, or create and edit zip files that can be read by external applications.
• Compress Files and Streams
  Store resources in compressed files, download them efficiently, and then load them on the client side. You can also compress streams and bypass files altogether.
• Encrypt Data
  Encrypt the data you save in isolated storage for additional security.
• Perfect for XML Data
  XML is one of the most common formats used by Web applications. XML data typically compresses to about 10% of the original size.
• Get More Mileage Out of Isolated Storage
  WPF applications don’t have access to the file system; they only have access to a limited amount of isolated storage. Use this storage efficiently by compressing the data.