Understanding Gutter Coil Alloys: 3105 vs 3003 Aluminum
Not all aluminum gutter coil is the same. The alloy—the combination of aluminum with other metals—changes how the material performs, how easy it is to work with, and how long it lasts.
The two most common gutter coil alloys are 3105 and 3003. They're similar, but they have important differences. Choosing the right alloy for your project matters.
This guide breaks down the differences and when to use each.
What Is an Alloy?
Pure aluminum is soft and not strong enough for gutter applications. Mixing aluminum with other metals (copper, manganese, magnesium, etc.) creates alloys with different properties.
Aluminum alloy designations like "3105" are standardized by ASTM and industry standards. The designation tells you the exact composition of the alloy.
3105 Aluminum Alloy
3105 is the most common aluminum gutter coil alloy. It's the default spec for standard residential and commercial gutters.
3105 Properties
- Strength: Medium-strength aluminum
- Workability: Good—easy to brake and bend
- Corrosion Resistance: Excellent—resists corrosion in most climates
- Cost: Standard, baseline pricing
- Industry Use: Dominant alloy for gutter coil
3105 Advantages
- Cost-effective (baseline pricing)
- Good corrosion resistance
- Easy to work with in brakes
- Excellent for residential and light commercial
- Standard material—widely available
3105 Disadvantages
- Not as strong as 5xxx series alloys (rarely an issue for gutters)
- Not as easy to form as 3003 for complex profiles
When to Use 3105
Standard residential guttering—this is your default choice. 3105 performs well, costs right, and is available everywhere.
Commercial gutters with standard profiles—3105 handles commercial loads without issue.
Most jobs use 3105. If your supplier doesn't specify alloy, you're probably getting 3105, and that's fine.
3003 Aluminum Alloy
3003 is slightly softer and more ductile than 3105. It's easier to form and work with, but slightly less strong.
3003 Properties
- Strength: Medium-strength, slightly lower than 3105
- Workability: Excellent—very easy to brake and form
- Corrosion Resistance: Excellent—similar to 3105
- Cost: Slightly higher than 3105 (maybe 5-10% more)
- Industry Use: Specialty applications, custom profiles
3003 Advantages
- Very easy to form and work with in brakes
- Excellent for custom profiles and complex shapes
- Nearly identical corrosion resistance to 3105
- Good for contractors who do lots of custom fabrication
- Minimal cost difference from 3105
3003 Disadvantages
- Slightly less strong than 3105 (rarely an issue)
- More prone to denting during handling
- Not as commonly stocked as 3105
When to Use 3003
Custom profile work where you're forming specialty shapes—3003's workability makes it easier.
Contractors with older or less powerful brakes—3003 requires less brake force than 3105.
Projects where you need tight bends or complex curves—3003 forms more easily.
Comparing 3105 vs 3003 for Gutters
Strength
3105 is slightly stronger. But for typical gutter applications, both are more than adequate. Unless you have unusual load conditions, strength difference is negligible.
Workability
3003 is easier to work with. If you're forming custom profiles or using an older brake, 3003 is more forgiving.
3105 requires a bit more brake force but most modern brakes handle it without issue.
Corrosion Resistance
Both have excellent corrosion resistance. In typical residential and commercial climates, they're essentially equivalent.
In coastal or extreme environments, both perform similarly. If you need enhanced corrosion resistance, move to 5xxx alloys.
Cost
3105 is standard pricing. 3003 is slightly more expensive (maybe 5-10% higher).
For most jobs, the cost difference is negligible. On large projects, it might matter.
Availability
3105 is more commonly stocked. 3003 requires ordering from suppliers who carry specialty alloys.
If you need specialty alloy availability, work with a factory-direct supplier who can stock both.
Other Aluminum Alloys for Gutters
3105 and 3003 cover 95% of gutter applications. But other alloys exist for specialty applications.
5005 Aluminum
5005 is a higher-strength alloy with slightly better corrosion resistance than 3105. It's sometimes used in marine or extreme environments.
More expensive than 3105. Rarely needed for standard gutters.
5052 Aluminum
5052 is high-strength with excellent corrosion resistance. It's used in marine applications or extreme salt-spray environments.
Significantly more expensive than 3105. Overkill for most applications but necessary in harsh coastal environments.
1100 Aluminum
1100 is pure aluminum, soft and easy to form but low strength. Sometimes used in specialty applications, but not recommended for structural gutters.
Practical Recommendation: Which Should You Specify?
Default Choice: 3105
Specify 3105 for most projects. It's the standard, it performs well, it's cost-effective, and it's widely available.
Unless you have a specific reason to use something different, 3105 is the right choice.
Custom Profile Work: 3003
If you're doing custom profile fabrication or have constraints with your brake equipment, consider 3003.
The slight workability advantage of 3003 can save time and reduce scrap on complex jobs.
Marine/Coastal: 5052
If you're in a coastal area with salt spray, 5052 offers better long-term corrosion resistance than 3105.
The cost premium is worth it for buildings expected to last 40+ years in harsh salt-spray conditions.
Hybrid Approach
Many contractors stock 3105 as their standard and order 3003 or specialty alloys when projects specifically require them.
This maximizes inventory turnover while maintaining flexibility for custom work.
Getting the Right Alloy from Your Supplier
When you order gutter coil, specify the alloy. Don't leave it to chance.
Your specification should read: "20 oz, 3105 aluminum, K-style profile, 16-inch width, brown paint finish."
Or: "22 oz, 3003 aluminum, custom box profile, 24-inch width, Kynar 500 finish."
Clear specs prevent surprises when material arrives.
Asking Your Supplier About Alloys
Good suppliers can clearly explain alloy differences and make recommendations based on your application.
Questions to ask:
- What's the standard alloy you ship?
- Can you provide 3105 vs 3003?
- Do you stock specialty alloys like 5052?
- What's the cost difference between alloys?
- What alloy would you recommend for this application?
A supplier who can answer these questions confidently understands material science. One who says "we just sell gutters" doesn't.
Ready to Order the Right Alloy?
Get a quote for aluminum gutter coil and specify your alloy requirements. Exterior Distribution stocks both 3105 and 3003 aluminum, custom profiles, and specialty alloys for any application. We'll ensure you get exactly what you specify.