All Mopflies.com flies are tied with Tungsten beads. The reason is that tungsten beads are almost three times heavier than more common brass beads. Although tungsten beads are a lot more expensive than brass beads, it is important to have the additional weight at the head of the fly as opposed to adding split shot to your line or tippet. The fly or jig needs to have the most natural drift possible and having the weight at the head of the fly gives you that advantage.
More than 90% of a trout's diet comes from food sources below the surface. The same is true for other species like crappie, bluegill, and carp. In most cases, you want the Mop Fly to be fished near the bottom, so tungsten provides the quickest sink rate which is especially beneficial in swift flowing water. In warm water environments like lakes or ponds, a quicker sink rate is also preferred (regardless of whether you are fishing the Mop Fly with a fly rod or spinning rod).
There are some cases where you may need a slower sink rate, and that can be accomplished by having either no bead head on the fly or using a brass bead head. But in all other cases, tungsten beads are the preferred choice.
Get your fly down to the fish with tungsten. The difference is noticeable, and you will see the difference in your fish count!