I know that the traditional material for cylinders is a branded concrete form product called Sonotube, which is essentially round cardboard but isn't necessarily available in reasonable sizes. Home Depot carries a Sakrete form but I've heard that these aren't always in the best condition. In looking around I've seen several other similar options and I'm wondering if one of these would be a good or bad choice to build a sub around.
Commercial HVAC ducting, I think this is usually aluminum. There's a build thread out there but it strikes me as worryingly thin.
PVC pipe. Not sure where to source this stuff.
HDPE based concrete form (Ceme-Tube). Might be a promising choice?
Cylindrical plywood rings. Rather expensive and need to be glued to get a tall cylinder, but maybe a much more robust and inert choice.
I'm really interested in the ceme-tube, although I haven't gotten pricing info yet. Is there a wrong answer here?