PVC plastic would be the best insulator.
There are various densities of PVC, so this is impossible to answer.
A flexible pencil
Paper is flexible because you can bend it. That is how I know instead of going on the internet.
Define a system
The Shore A hardness scale has been used for decades to characterize the relative hardness of flexible PVC. Rigid PVC should be measured by the Shore D durometer.
Depends on what king of PVC and what's the concentration of the acid. For example the 35% HCl damages the flexible PVC on 50°C, but the rigid PVC not... (The flexible PVC become rigid I think.)
plastersizers
The smaller sizes are more flexible. Colder temps affect flexibility.
The smaller sizes are more flexible. Colder temps affect flexibility.
None. PVC is not made to be glued to concrete.
Bemakjhs
PVC pipes are strong and durable, yet flexible enough to bend without breaking, allowing them to endure earth movement.
Carbon, hydrogen, chlorine. If it's flexible, there's probably some oxygen in there as well. Rigid PVC is poly(vinyl chloride), where vinyl chloride is ethene with one of the hydrogens replaced by a chlorine atom. Flexible PVC ... sometimes called simply "vinyl" ... has additives like octyl phthalate (which contains carbon, hydrogen, and oxygen) that keep the polymer swollen and flexible.
0.14 - 0.17 W*m^-1*K^-1
I have never seen flexible PVC. However It does not seem like a good idea to use flexible piping for the suction side of the system especial y with the weight of fill on top of it. even on the pressure side there could be problems with the possibility that the weight of the fill on top of the tubing would eventualy flatten it.
PVC in its native state is fairly rigid. Flexible PVC ("Vinyl") is made by adding plasticizers to the material. In the old days, compounds such as octyl phthalate were simply added into the mix and would slowly leach out or evaporate over time; this is why old vinyl used to get brittle after a while. The modern method is to introduce internal plasticizers which are actually part of the (mostly) PVC molecule; these cannot leach out and keep the vinyl flexible.