A wrap panel in Microsoft® Expression Blend™ is similar to a stack panel, but it allows elements to be placed on multiple lines. When an element overflows off the edge of the stack, it will not be clipped, but instead will be wrapped to the next line. As you add more child elements, the wrap panel will continue to wrap the elements until it runs out of space. Only then will it clip the elements.
By default, the elements within a wrap panel are placed horizontally from left-to-right, top-to-bottom, but you can also place them vertically from top-to-bottom, left-to-right. Change the Orientation property for a wrap panel within the Properties panel under Layout.
Add a wrap panel to a document by using the Asset Library or the layout container button on the Toolbox.