The Ultra Ball (Japanese: ハイパーボールHyper Ball) has a 100% higher chance to catch a Pokémon than a regular Poké Ball, and a 33% higher chance than a Great Ball. It has a catch multiplier of 2.0.
This is a Black Ball with a Yellow Stripe. It has a black and yellow top, often with the yellow forming an "H" on the top of the ball. In Japan, It is called a Hyper Ball, hence the "H" pattern on top. Like the other balls (except Heal, Quick, Dusk, Cherish and Dram Balls) it has white in the lower part.