The Force Field Block is a block that comes in two colors, Blue and Red. The team of the color say, Red is able to pass through the Red Force Field Block but to a blue team member it will act as a solid block and vice versa for the other team. This block is the only block that you can place that you can see through making it ideal for windows in bases forts and lava viewing pads.
The Engineer is able to place both Red and Blue force fields regardless of the team color, this is ideal for making bridges as you build a bridge of the oppisite team making it solid for you but air for the other team, such uses for this are bridges over lava which you can walk over harmlessly while they fall into the lava when they try.
Both types of force field.