I believe the closest analog you'll find for human sized PVC pipe that wouldn't be PVC pipe is called concrete form tubes, sometimes under the brand name Sonotube. The Home Depot version is called Sakrete form tube. It's going to be lighter than PVC of human size, but that doesn't mean it will be light. As it is constructed of cardboard, it would be easily painted white with matching lettering. If you wanted to hide the joints, fabric could be glued at the knees, elbows, etc, but you're going to have a challenge finding a skinny enough human torso to fit inside the typically-available Sonotube diameters.
You could use some sort of cording that runs from the knee joint through the thigh bone up through the torso to a shoulder support to help manage the weight. If you're using a healthy firefighter for the inner-human, it would not be too heavy, I believe.
The torso could be a suitably sized plastic rubbish bin, also painted white. If you plan to encase the human's head as well, a portion of a smaller cylindrical rubbish bin would also work. It's starting to look a bit like a lego character in my alleged mind.
This photo is the 8" size, although other smaller sizes are also available. Some larger construction businesses may have discards if you have contacts in the area.