Vilene 220/304 iron on medium, fusible interfacing is white and 90cm wide.
Use your iron (shiny side of the interfacing against the wrong side of the fabric) in order to bond it to the fabric and stiffen it.
It isn't difficult to use and adds great 'body' to a fabric. It changes the drape of the fabric giving it a 'crisper' feel. It's always a good idea to use a piece of scrap fabric with an 'unfamiliar' interlining to check that this is the effect you're looking for.