Source: Technology Guide, pg(s). 45
A force field is an invisible, intangible field of force generated around the wearer of a pair of slender, silvery bracelets. When the force field is activated, it pierces the wearer's arms with dozens of tiny biofeedback needles which interface with the nervous system, creating a barrier that blocks solids and liquids but not gases or light. Force fields come in nine different grades; the higher a force field's grade, the more durable it is and the longer it can last before a recharge is required.