Every bishop is required to have a mitre made of white linen or silk, which is used on certain Pentitential Days and for Requiem Liturgies. It is called the simple or simplex mitre. The Pope, also, uses such a mitre, but his is more ornate, because of his unique Office. The adjacent photograph shews Pope Benedict wearing the Papal simplex mitre at yesterday's Ash Wednesday Mass and Penitential Procession in Saint Peter's Basilica.
Instead of being made of white linen, the Papal simplex mitre is made of cloth silver, namely fabric of a silk or linen ground, but interwoven with threads of silver, running crosswise through the fabric. Such fabric has a slight glitter when struck by light. Around the perimeter of the Papal simplex mitre is a gold braid, which usually also ornaments the lappets, or tails of the mitre, as is shewn here.