These barrels are cold-hammer forged, which is the same process that real firearm barrels undergo. This process creates a very consistent bore, and PDI states that this gives the barrel a tolerance of +0.002mm. This is currently the highest quality in the Airsoft industry for easily accessible stainless steel barrels.
The material is 304 Stainless Steel. This Steel is harder than most barrels and has superior corrosion resistance. Additionally, PDI barrels are very well known for their straightness and quality control.
The bore is coated with Palsonite, which is a technically advanced surface treatment that changes the molecular structure of the SUS304 Stainless Steel. This results in an extremely hard and smooth bore with remarkable abrasion resistance.