Physler

Physlers are a custom testing element in Portal 2, created by Felix Griffin (based on a Portal map by Omnicoder.

They are modified Fizzlers which do not reset the Portal Gun or destroy objects. Rather, any physics objects besides the player are blocked, as if by a wall, while lasers, tractor beams, and Hard Light Bridges can move right through.

Manual Creation

These fields can be created similarly to Fizzlers, but using a func_brush instead of a trigger_portal_cleanser, with material effects/physler. The blocking is accomplished with another brush textured with tools/trigger, tied to a trigger_physics_clip entity.