The actress set up her Golden Hat Foundation in 2011, and wanted to raise its profile through an event, reports contactmusic.com.
Winslet invited her A-list pals including Jude Law, Christina Aguilera and Demi Moore to don her beloved trilby for a photo book. The actress was stunned at the positive response from her Hollywood friends.
"So I came up with this idea... to send my favourite beaten-up trilby to as many well-known people as I could track down and ask them to photograph themselves wearing it," she added.
"I would then make a book of self-portraits... Amazingly, nearly every person I asked said yes," she said.