Buyers sourcing steel coil for roofing and panels often ask whether to order PPGI or plain galvanized (GI) coil. They share the same galvanized base, but the paint layer changes cost, appearance and use. This guide from ChinaCNU Steel — a China PPGI and GI coil manufacturer — explains the difference and which to choose.
What Is GI (Galvanized) Coil?
GI coil is steel hot-dip coated with zinc (Z40–Z275). It is bare metallic-grey, corrosion resistant, and ready for forming, welding or further processing such as colour coating.
What Is PPGI Coil?
PPGI (Pre-Painted Galvanized Iron) is GI coil that has been cleaned, chemically treated, primed and finished with a coloured topcoat (PE, SMP, HDP or PVDF) in any RAL colour. It is essentially “galvanized + paint,” supplied ready to roll-form into finished coloured products.
PPGI vs Galvanized: Side-by-Side Comparison
| Property | GI (Galvanized) | PPGI (Pre-Painted) |
|---|---|---|
| Surface | Bare zinc, metallic grey | Coloured paint over zinc |
| Colour options | None | Full RAL range, custom |
| Corrosion resistance | Good (zinc only) | Better (zinc + paint barrier) |
| Ready to use | Needs painting for finished look | Finished, roll-form directly |
| Cost per ton | Lower | Higher (paint added) |
| Typical use | Ducts, framing, base for PPGI | Coloured roofing, wall panels, appliances |
Which Should You Choose?
Choose GI when you will paint or process the steel yourself, or for non-visible structural parts where colour is irrelevant. Choose PPGI when you need a finished, coloured surface straight off the coil — coloured roofing sheets, sandwich panels, wall cladding and appliance housings. If you need maximum corrosion life, consider a galvalume (aluzinc) base, and see our galvalume vs galvanized comparison.
Frequently Asked Questions
Is PPGI just painted galvanized steel?
Yes. PPGI is galvanized (GI) steel with a factory-applied, oven-cured coloured paint system, which also adds an extra corrosion barrier.
Does PPGI last longer than GI?
Generally yes — the paint layer protects the zinc, and the colour stays for the life of the coating (10–25 years depending on PE vs PVDF).
Can I order GI and have it colour-coated later?
Yes, but ordering finished PPGI is usually more economical and consistent than coating small lots separately.
Do you supply both PPGI and GI?
Yes. ChinaCNU manufactures both. Send your spec, colour and tonnage for a 24-hour FOB Tianjin or CFR quote.
Not sure which to order? Tell us your end product and we will advise GI, PPGI or galvalume and quote within 24 hours.