The one-line answer to 3105 vs 3003 aluminum: 3003 is the general roofing and cladding workhorse; 3105 is the stiffer, pre-painted coil grade for when a panel has to span further. 3105 adds magnesium on top of 3003's manganese, which gives it more strength at the same gauge — the difference between a panel that stays flat and one that oil-cans between supports.
Both are aluminum-manganese (3xxx) sheet grades, non-heat-treatable, and both are normally supplied as coil, often pre-painted. The choice is span against price.
The numbers
| 3003 | 3105 | |
|---|---|---|
| Manganese | 1.0 – 1.5% | 0.30 – 0.80% |
| Magnesium | — | 0.20 – 0.80% |
| Typical tensile (H14/H24) | ~160 MPa | ~170 MPa |
| Typical yield | ~130 MPa | ~140 MPa |
| Coating | optional | usually pre-painted |
| Formability | excellent | good |
| Relative cost | lower | slightly higher |
The magnesium in 3105 is the whole story: it raises strength and stiffness a notch above 3003 without going to 5052 prices, and it is the reason 3105 is the standing-seam and cladding coil grade.
Where 3003 wins
- General roofing and gutter coil on short spans, where 3003's strength is plenty and the price is right.
- Deep-drawn or severely formed parts. 3003 forms more easily than 3105, so cookware, duct and drawn work stay on 3003.
- Bare (uncoated) sheet. Where the part is painted after fabrication or left bare inland.
Where 3105 wins
- Standing-seam and long-span roofing. 3105 spans further at the same gauge, so it is the choice for architectural cladding and standing-seam profiles.
- Pre-painted wall and fascia panels. 3105 is the standard pre-painted coil grade, supplied with the coating already applied.
- Where the coil goes straight onto a roll former. The higher stiffness holds the profile shape through forming and in service.
The coating question
Because 3105 is normally pre-painted, the coating decision matters as much as the alloy. Two rules worth knowing:
- Polyester for general roofing; PVDF (70% Kynar) for facades and anything with a color warranty. Film build is normally 20–25 µm for polyester and 25–28 µm for PVDF over a primer.
- A conversion coating plus primer is not optional for exterior service. Skipping the primer is the usual reason a two-year-old roof chalks.
These rules apply to 3003 when it is coated too — they are about the coating system, not the alloy — but 3105 is where they most often come up because it is the pre-painted grade.
How to choose
| Your project | Choose |
|---|---|
| Short-span roofing, gutter, drawn parts | 3003 |
| Standing-seam, long-span cladding | 3105 |
| Pre-painted facade with color warranty | 3105 + PVDF |
| Severely formed or spun part | 3003 |
The practical rule: if the panel has to span and you want it pre-painted, 3105; if it is short-span or heavily formed, 3003. Ask for both prices at your gauge before deciding — the gap is often small enough that 3105 wins on the strength it buys.
What gets ordered wrong
The first error is bending pre-painted coil on too tight a radius. The paint cracks before the metal does, so the bend radius has to be agreed with the coater, not assumed. This is a 3105 problem in practice because it is the coated grade.
The second error is specifying a coating without a color warranty on a facade, then wondering why it chalks. For visible cladding, PVDF with a written warranty is the difference between a roof that lasts and one that fades in two years.
The third error is treating 3105 as a marine or structural alloy. It is a roofing grade, not a hull or load-bearing alloy. For salt or structural duty, move to 5052 or 6061.
Bottom line
3003 for general roofing and forming, 3105 for long-span pre-painted cladding. The magnesium in 3105 buys a little extra stiffness and span at a modest price, and the real decision is usually the coating system, not the alloy.
See the 3003 and 3105 grade pages for the property tables. If you are quoting a roof or facade, send the panel profile and span — we will tell you which gauge and coating the job needs.