The sun's magnetic field spins opposite directions on the north and south poles. These oppositely pointing magnetic fields are separated by a layer of current called the "heliospheric current sheet." Due to the tilt of the magnetic axis in relation to the axis of rotation of the Sun, the heliospheric current sheet flaps like a flag in the wind.
The flapping current sheet separates regions of oppositely pointing magnetic field, called sectors. As the solar wind speed decreases past the termination shock, the sectors squeeze together, bringing regions of opposite magnetic field closer to each other. The Voyager spacecraft have now found that when the separation of sectors becomes very small, the sectored magnetic field breaks up into a sea of nested "magnetic bubbles" in a phenomenon called magnetic reconnection.
The region of nested bubbles is carried by the solar wind to the north and south filling out the entire front region of the heliopause and the sector region in the heliosheath. This discovery has prompted a complete revision of what the heliosheath region looks like. The smooth, streamlined look is gone, replaced with a bubbly, frothy outer layer.