Hi there Jyrki
For many years I tried dozens of products including the Jaguar one which eventually they took off the market.
Since then I found the perfect one it’s From Auto Glym its a twin pack one Cleaner one water proof PLEASE follow the instructions to the letter. What I found best was to use cling film instead of plastic sheet.

http://www.ebay.co.uk/itm/AUTOGLYM-CABRIOLET-CONVERTIBLE-FABRIC-HOOD-CLEANING-KIT-/162376771214