From Science via NatureNews:

The amber samples are between 70 and 85 million years old, and come from a site called Grassy Lake in western Canada that was once home to a conifer forest. The site is well known for the wide range of insects found preserved in its amber.

Palaeontologist Ryan McKellar and his colleagues at the University of Alberta in Edmonton were keen to find out whether any feathers had been preserved, so they sifted through more than 4,000 of the amber inclusions held in museum collections. Once feathers were found, the samples were mounted on slides and polished, before being analysed using microscopy. The team reports the 11 feathers identified, as well their range of structures, today in Science¹.