Blocks with shields require more damage before they are destroyed.
A block with a blue outline means you will have to do 3 points of damage to destroy it.
A block with an orange outline means you will have to do 5 points of damage to destroy it.
Different Bubs (balls) will do different amounts of damage when they hit a block. Some will do 1 point, while others can do up to 5 points of damage per hit.
Using certain Powerups will also increase the amount of damage your ball does when hitting a block.