When working with magnets in industrial or marine environments, you rarely get a perfect, lab-grade surface. There may be painted hulls, corroded beams, curved pipes, marine growth, or simply rough or uneven steel. All of these introduce what's commonly referred to as airgap — any form of material or space that separates the magnet from the steel surface.

To sum up, "airgap" can be:

• Paint or epoxy coating

• Rust or scale

• Curvature of the steel surface

• Marine growth or biological matter

• Surface unevenness

• Dust or debris

Magnetic field strength decreases rapidly with distance from the magnet. To simplify the physics behind it, the strength can be said to reduce by the cube of the distance, or B is proportional to 1/s^3, where B is the field strength and s is the distance.

On top of that, the force is proportional to the square of the field strength. This means that the force drops with the distance to the power of six, or F is proportional to 1/s^6, where F is the magnetic force.

Now, the ideal mathematical condition above only applies for a very small magnet (a so-called ideal dipole), or far away from a magnet, where the geometry of the magnet itself does not shape the field locally. While it's true that all magnets are sensitive to airgap, there are important differences between various types of magnets due to their different internal geometry.

Pot magnets are a common and inexpensive magnet type. They are usually round and consist of a central magnetic core placed inside a steel pot. work by forming a closed magnetic circuit between the steel casing (the pot) and the central magnetic core. The rim of the pot is one magnetic pole, and the core is the other. This tight circuit design makes pot magnets very strong — in ideal, airgap-free conditions.

However, that same tight circuit is exactly why pot magnets are extremely sensitive to any separation. The magnetic field is highly concentrated between the rim and the core, and it doesn’t extend far beyond the face of the magnet. As soon as there’s an airgap, the magnetic circuit breaks down, and the holding force drops off dramatically.

In contrast, sandwich magnets (also known as through-pole or dual-pole magnets) are designed with the poles on opposite steel elements, sandwiching the magnetic material. This configuration creates a more open magnetic field that extends further from the magnet surface.

That means sandwich magnets are inherently more tolerant of airgaps. Even if there’s paint, corrosion, or some marine fouling, the magnet can still maintain a usable field strength and holding force. That’s why all of Blumags's magnets are sandwich-type designs — because in real-world conditions, airgaps are the rule, not the exception.

Even though sandwich magnets are more forgiving, minimizing airgap is still key to getting the best performance:

• Scrape off loose paint or corrosion where possible

• Wipe away marine growth or debris

• Aim for flat, direct contact when placing the magnet

These simple steps can dramatically improve holding force and reduce the risk of slippage or failure in critical applications.

Airgap is one of the most important, and most underestimated, factors in magnetic performance. Pot magnets may look powerful on paper, but in real-life applications involving paint, corrosion, or curvature, their performance can drop off sharply. That’s why Blumags uses sandwich-type magnets across the board — to deliver reliable, consistent holding force even under less-than-ideal conditions.