Solid Wire vs Flux Cored Wire - Which welding wire to choose

10th March 2025

Choosing the right wire when you're welding is a complex but an important step before starting your MIG/MAG welding project. The main wire that you're likely to select are Flux Cored Wire or Solid wire. These two specific types of wire are different and suited to specific types of welding projects and specific conditions.

While solid wire or MIG wire is known for its consistent and smooth weld, flux-cored wire is a must have when you are welding outside for example, in a dirty or windy environment.

These wires also have some similarities and other specificities that you need to bear in mind while preparing your welding machine. In this article, after presenting the characteristics of these two types of wire, we'll go deeper into the differences that will help you select one wire or the other for your next welding project.

What is a Flux-cored wire?

Gas shielded and self shielded flux cored wire are two specific types of flux core welding wire.

Unlike gas shield wires, self-shielding cored wires don't need external shielding gas. Indeed, when flux from the wire is burned, it generates a gas that protects the weld pool.

Gas-shielded flux-cored wires are more suitable to weld thicker material or in out-of-position welding applications. During processes, the flux coating solidifies more quickly than the molten weld material, creating a slag shelf that helps support the molten pool. This makes these processes more suitable for welding overhead or vertically up.

One of the best flux cored welding wires for your project is Esab Coreshield 15 0.8mm 4.5kg. This flux cored welding wire is recommended for its versatility, offering reliable performance in both indoor and outdoor conditions, and its ability to handle mild steel with ease, making it suitable for a wide range of general fabrication and repair work.

What is a Solid wire/MIG wire?

Solid core wires are used by MIG/MAG welders for filler metal. This welding technique requires shielding gas, most commonly 80% argon and 20% carbon dioxide, delivered from a gas bottle. The aim of this shielding gas is to protect the molten weld pool from contamination that can come from the surrounding of the weld. When welding outdoors with a solid wire, in windy conditions it's recommended to use a windshield to prevent the wind from blowing away the shielding gas while welding.

To increase the life of the welding contact tip, help the electrical conductivity and prevent oxidation, some wires are plated with copper. These cables are called mild steel solid wires. A good Mild Steel MIG Wire that you can use for your next project is the Radnor Precision G3Si 1.0mm Mig Welding Wire 15kg Plastic Spool.

The similarities between solid wire and flux cored wire

These two types of wire can be used as a filler metal for wire welding processes. As they are perfectly bound on either metal or plastic spools, it's easy to setup MIG welding wire on a MIG/MAG welding machine. They both carry current, supply the filler material into the weld gap and support the welding arc.

Thanks to their similarities, you can use both of them for your MIG/MAG welder, but bear in mind that the MIG welding wire size is something you need to select carefully. Plenty of metal can be welded with these two types of wire such as steel, aluminum, steel or stainless steel depending on the type and size of the wire.

The differences between solid wire and flux cored MIG welding wire

Even if these two types of wire have a lot in common, there are still some differences that you need to bear in mind before choosing one or the other for your next welding project. The main differences are concentrated around the appearance, the price, the penetration, the structure and the polarity.

Appearance

Appearance can be an important factor when you begin a welding project, even more when you are working with thin metals. If you wish to create a high quality weld with little splatter, smaller heat-affected area and reduce the chance of burn-through, it's usually recommended to use solid wire. A good example of it is for welders who are going to work on car bodywork or welders who work with thinner sheet metal applications.

Environment

As previously discussed, the environment in which you are welding can be an important factor in the choice of your welding wire. In a windy environment and without a windshield, we will not advise you to use a solid wire or gas-shielded flux-cored because they are more difficult to use. In this case, shielding gas issues can produce porosity visible in the weld bead.

Self-shielded flux-cored wires are the solution in this case, and since you don't need to carry an external shielding gas bottle, it's also going to be easier to carry and transport to your welding spot. We'll recommend using flux-cored wire for agriculture applications for instance, where you need to move a lot to weld or repair a farming plant for example, and sometimes, in outside conditions.

Moreover, Flux-cored wire can weld dirtier materials with higher levels of rust, mill scale or oil. De-oxidizing elements will trap those elements in the weld pool and hold them in the slag coverage.

Wire penetration

These two types of wire show different penetration levels for the same amperage. If you are working on thicker material and you want to have the best penetration while using fewer amps, the flux cored arc welding wire is going to be the solution. They are producing more heat in a concentrated area which helps to weld thicker elements. But this concentrated heating can also be a negative side because you can easily burn through thin metal.

But penetration can't only be seen as a strength. You can find the minimal strength of your wire on its packaging with its AWS Classification. When people say that welding wire flux cored creates more robust welds, they refer to its deeper penetration in thicker materials, not the weld's tensile strength itself.

Cost and productivity

Even if a flux-cored wire is more expensive in itself than a solid wire, it can help you gain productivity. Indeed, when welding with a flux-core wire, you'll not need to clean and prepare the steel, this can save you time depending on the situation.

Flux-cored wire also has high deposition rates and an increase penetration on the sidewalls. While spending more money on a flux-cored wire, you'll gain time during your welding project. Flux-cored wires can be more cost efficient in industrial case welding while solid wire is more cost efficient for occasional hobby welders.

Feedability and safety

Wire feeding can be something to bear in mind depending on the welding application, and these two types of wire, because of their structure, have different feedability. Because of its softness, a flux cored wire can be harder to feed with regular U-grooved rolls. Instead, you might need to use knurled or W rollers. They are using small knurls or "teeth" to tightly grip the soft wire and feed it constantly.

In contrast, solid wires are more rigid, eliminating the need to address these concerns. They can be fed using a standard U or V-grooved roller, which typically comes included with your welding equipment.

You also need to bear in mind that safety is one of the most important things while welding. Safety shouldn’t be negligible either if you work with Solid Wire nor Flux Cored Wire. While welding with this type of wires, the flux shields the weld and releases gas that protects the weld puddle, but it also releases toxic fumes. These fumes can cause fume fever for instance, and long term exposure can cause severe health consequences. Air fed welding masks like the Esab Sentinel A60 For Air Welding Helmet are a must have while welding.

While welding, you can also have welding spatter that can land on your hands or your body. Welding PPEs are mandatory during your welding project. You can find a large range of welding PPE such as welding gloves, or Auto-Darkening welding helmets on our website or in our local stores.