Best fit I found for atomizers ect seems to be 1/8" i.d. 1/4" o.d.
Lot of tubing is 3/16" o.d. and a bit loose in some parts though useable.
As to type of tubing,lots of scuttlebut on this.
If money is no option found this stuff has an appealing color and very low CO2 permeability..but at over $1/ft certainly not economical..
After 6 months using it (took awhile to find the right size locally) no brittleness as I found in standard PVC..
got to admit some of the appeal is the chartreuse color.. Odd I know..
There is no "need" for this quality or price.
Only real arguable tubing to avoid is silicone (relatively high CO2 permeability but really only applies to high pressure and long runs and may only "waste" a few $'s in CO2) unless you have glass outlets. Then is is almost a necessity, but save it for the last mile so to speak..
Keep in mind most of these PVC type tubing is only rated to about 30-40psi..
High pressure tubing is more the poyurethane (stiff) water line type stuff and "I" found it really doesn't fit well w/ a lot of stuff. Rating in these sizes is usually well beyond 40psi..
Dirt cheap though..