Propane “quality” refers to the difference between how propane is refined and processed, and in particular to the proportion propylene, butanes and ethane. This does not mean that one propane type is better than another.
In the United States, we mostly use what is called HD5 propane. Technically, this only means that the gas used is made up of:
- 90% propane,
- maximum 5% propylene, and
- no more than 5% butane and methane.
HD10 propane simply has more propylene in the mixture (up to 10%). It is mostly used in California. This type of propane mix works normally with domestic appliances but it lead to engine components sticking when used for some engines or vehicles (propylene is used for plastics).
Commercial propane is yet another type of mixture between propylene, butanes and methane with propane but does not fall into either HD5 or HD10. However, its use is similar to that of HD10 propane: many refineries use it in processes but it is not used in vehicles.
This does not mean that there is a purer kind of propane, just that what is mixed with propane comes in different proportions. All residential propane is HD5 and no propane company sells “purer” propane. HD5 propane is the highest grade American consumers have access to.