The Personal Defensive Shields of the Dune Universe are not round projections of force, but full-body shields which permit objects to pass through them, only slowly. An object attempting to pass through a planar field at a right-angle vector speed of more than the strike speed is faced with resistance which grows more intense as the fourth power of the velocity. When the speed is sufficiently high, the field becomes essentially solid to the impinging object. Shields have varying "strike speeds" -- that speed at which a normal object can pass a planar Holtzmann field -- that depends upon the electromagnetic admissions spectrum of the planar field. It is never less than 5.8 cm/s for one-angstrom fields, and increases only to 9.3 cm/s for all-absorptive fields. Typical shields have a strike speed of about 7 cm/s admitting most visible light, x-rays and gamma rays.

Against ranged attacks of high velocity (bullets, rockets, grenades, etc.) the shield is extremely effective. Slow velocity slug-throwers do exist, but are rare and not very effective.

Defensive shields react explosively upon contact with the coherent light of laser weapons. When coherent light impinges upon a planar effect field from either surface, all pseudo-matter bound in the shield is instantly converted to real matter. This converted matter then converts explosively to pure energy. Fortunately the actual mass of a planar field is quite small, on the order of .005 g for a personal shield. Thus, a typical personal defensive shield if touched by a laser beam, would result in an atomic blast with a power of .1 kilotons. The center of this blast is quite erratic, sometimes originating within the shield, sometimes within the laser weapon, sometimes both, with no way to determine it beforehand, making the tactic of using laser weapons to take out shields explosively suicidal.

The shield can also be used as an active defense like its medieval counterpart. However, because of its full coverage, it can be used not only to block incoming attacks but also to parry them. A skilled fighter can use his shielded arms to parry an incoming weapon attack without fear of being injured in the attempt.

However, the Holtzmann planar field is not impermeable, and several shield-fighting styles have developed to exploit this weakness.

Moreover, a very skilled combatant is familiar with the workings of a shield, and can compensate in such a manner, as to make the shield's defensive value less than optimum.