Why can a magnet still hold through paper or your hand?
― It's actually iron that can block magnetism
Slip sheet after sheet of paper between a fridge and a magnet, and the magnet still won't fall. Press your palm against the fridge, and you can still feel the pull tugging through your fingers. To a magnet, paper, skin, plastic and aluminium are almost all "as good as nothing." And when you actually want to block magnetism, the material you reach for isn't something magnets ignore — it's iron, the very thing they stick to best.
You stick a school flyer to the fridge door with a magnet. You slip in another sheet, then another — and the magnet still holds.
Now press your palm flat against the fridge and bring a magnet up on the other side. You can feel it being pulled through your hand toward the fridge, right through your fingers.
So what can a magnet's pull pass through, and what can actually stop it? It's a surprisingly tricky question when a kid asks.
The answer splits into two broad cases
Paper, skin, wood, glass, aluminium — for all of these, magnetism passes through almost as easily as through a vacuum. So the pull travels through as if nothing were there at all. When it feels weaker, that's not the material's fault — it's simply because the magnet has moved further away.
Iron is a special material that lets magnetic force through thousands of times more easily than air does. The magnetic field takes the shortcut, diving into the iron and looping back through it. As a result, almost none of the field makes it out the other side.
In other words, "a material magnets don't stick to" is not the same as "a material that blocks magnetism." It's the opposite: iron, the material magnets stick to best, is also the best at blocking magnetism. Let's go through it step by step.
Paper, skin and aluminium are all invisible to a magnet
Around a magnet, an invisible loop of force stretches out through space. It's the same pattern you see in science class when iron filings scattered on paper snap into curved lines.
How easily this field passes through a substance depends on the material — but this "ease of passage" turns out to be almost identical for paper, wood, glass, water, plastic, aluminium, copper, and even the human body. The difference from a vacuum is, in most cases, said to be only about one part in a hundred thousand. From the magnet's point of view, it makes no difference whether these materials are there or not.
This is where magnetism differs sharply from electricity. With electricity, materials split clearly into conductors (metals) and insulators (rubber, plastic). That's why rubber gloves keep electricity out. But for magnetism, there's almost no such thing as an "insulator." Look at the left side of Figure 1: the field's path cuts straight across whatever is sandwiched in between.
So why does stacking several sheets of paper weaken the pull a little? Not because the paper blocks it — because the thickness of the paper pushes the magnet a little further from the fridge. And a magnet's pull weakens astonishingly fast with distance. Just how fast, we'll work out in the final collapsible section.
To block it, wrap it in iron
Iron and nickel let magnetism through thousands of times more easily than a vacuum does. Magnetism, like a flow of water, strongly favors the easier path. Put an iron plate in the way, and the field's path stops going straight through the air — it dives into the plate and loops back to the magnet through the iron itself.
The right side of Figure 1 shows this. The lines get pulled into the iron plate, and almost none make it through to the other side. This is the principle behind magnetic shielding: precision instruments, and experimental equipment that must stay free of magnetic fields, are protected by enclosing them in boxes of iron or an alloy called permalloy.
Aluminium doesn't stick to magnets. But slide a strong magnet across a thick aluminium plate, and it slows down as if an invisible brake had kicked in. The moving magnet stirs up swirling electric currents in the aluminium, and those currents generate their own magnetic field that fights the motion. A stationary magnet feels nothing at all. The fact that it "only kicks in when moving" is the fun part of this effect.
Summary
A magnet's pull passes straight through almost everything around us. Paper, skin, glass, aluminium — to a magnet, they're all essentially the same as air; their very presence goes unnoticed. When the pull weakens as you sandwich things in, it's not because it was blocked — it's because the magnet moved further away. And when you truly want to block it, you wrap it in a material that magnets stick to well, like iron. You're turning the field's tendency to escape down the "easy path" to your own advantage.
What blocks a magnet isn't a material magnets ignore.
Iron, the material they stick to best, blocks them best too.
For more on the poles of a magnet themselves, see If you cut a magnet in half, do you get a magnet with only a north pole?, and for the puzzle of one-sided stickiness, see Why does a fridge magnet sheet only stick on one side?. For how the Earth itself acts as a magnet, see Why does a compass needle point north?.
- Stick a magnet to the fridge door and slip in sheets of paper one at a time, counting how many it takes before it falls. Then try the same thickness using a plastic sheet or a clipboard-style board instead, and see if it falls at about the same point. Different materials, same thickness — the results should come out close.
- Put a paperclip on a table and bring a magnet close enough to pull it. Then slide a spoon or a pair of scissors (something made of iron) between the magnet and the clip. If the clip stops moving, that's proof the iron blocked it.
- Slide an aluminium spoon or a coin between the magnet and the clip instead, and the clip still gets pulled. A metal that doesn't block magnetism — that's the clearest proof that "conducting electricity" and "conducting magnetism" are two completely different things.
Strong magnets can pinch and hurt if they catch your fingers, so always handle them with an adult. Small magnets have been reported to cause swallowing accidents, so keep them out of reach of young children.
Want to know more? ― Terms, formulas, and links to the textbookWe've marked which level each part belongs to, from junior high science to university-level specialty courses
- JHSCovered in junior high school science
- HSCovered in high school "Physics"
- HS+High school advanced content, or textbook sidebar material
- Univ.Not covered in high school — university-level specialty courses (electromagnetism, condensed matter physics)
- ResearchNot yet settled "textbook fact" even at university — an active research question
JHSTerminology: this phenomenon has names
- Magnetic flux: the spreading loops of force around a magnet, counted as a bundle. The arrows in Figure 1 trace out the path of this bundle.
- Permeability: a number describing how easily a substance lets magnetic flux through. Taking vacuum as 1, paper, water, aluminium and the human body are all close to 1, while iron reaches into the thousands.
- Ferromagnetic material: a substance like iron, nickel or cobalt that is strongly attracted to magnets and can itself become a magnet.
- Magnetic shielding: enclosing something in a high-permeability material so that flux can't get inside. The more fully it's enclosed, the more effective it is.
JHSHSChecking with numbers: how much weaker does a sheet of paper make it?
It's not the paper blocking the field — it's the extra distance that weakens it. Let's check this with numbers. Viewed from a bit of distance, the attractive force of a small magnet is known to fall off in inverse proportion to the fourth power of distance. Double the distance, and the force drops to 1/16.
| Thickness of one sheet of copy paper | about 0.09 millimeters |
| Original gap between magnet and fridge | about 1 millimeter (paint and sheet coating) |
| Relationship between force and distance (rough rule at a distance) | said to be inverse to the fourth power of distance |
| Thickness of 10 sheets of paper | 0.09 × 10 = 0.9 (millimeters) |
| Added to the original gap | 1 + 0.9 = 1.9 (millimeters) |
| Roughly how many times the original distance | 1.9 ÷ 1 = 1.9 (times) |
| Squared | 1.9 × 1.9 = 3.61 |
| Squared again, to get the fourth power | 3.61 × 3.61 ≒ 13 |
| Force as a fraction of the original | 1 ÷ 13 ≒ 0.077 |
With 10 sheets of paper, the pull comes out to roughly 1/13 of the original. The paper isn't absorbing the magnetism — moving just 0.9 millimeters further away is enough to cause this much change. Real magnets fall off a bit more gently than this, but it gives you the right feel: distance is everything.
| B | Magnetic flux density — how densely packed the flux is. Unit: tesla (T) |
| H | Magnetic field strength. Unit: amperes per meter (A/m) |
| μ | Permeability — the proportionality constant linking B and H. Unit: henries per meter (H/m) |
| r | Distance from the magnet. Unit: meters (m) |
HSHS+Why is iron so special?
HSInside matter, the motion and spin of electrons act like tiny magnets. In ordinary materials, these point every which way and cancel each other out, so no magnet-like behavior shows up from the outside. That's why paper and aluminium both sit at a permeability of almost exactly 1.
HS+In iron, a strong effect makes neighboring atoms line up their orientation with each other. This creates broad regions where the alignment is uniform, and even a weak field from outside is enough to make those regions suddenly expand and bring everything into alignment. The result is flux inside the iron that's thousands of times greater than the field applied from outside. Because this "aligning effect" is destroyed by heat, heating iron to around 770°C makes it stop being attracted to magnets.
Univ.Shielding is "rerouting," not "subtracting"
A magnetic shield doesn't erase flux. Viewed as a magnetic circuit, a high-permeability path has low magnetic resistance, so flux concentrates there — the same idea as current flowing preferentially through a low-resistance wire. That's why enclosing something in a box works better than just adding a plate. Materials are also chosen for the kind of field involved: high-permeability alloys suit steady fields, while conductors relying on eddy currents suit fast-changing ones. For experiments demanding extreme quietness, some methods use superconductors, which exclude magnetic flux entirely.
ResearchWhat we still don't fully understand
- Better magnetic materials usable at room temperature Research into strong magnets that don't rely on rare-earth elements continues worldwide, but no material has yet nailed both resource constraints and performance at once.
- How living things sense magnetic fields Experiments suggest migratory birds and sea turtles can sense the Earth's magnetic field, but exactly where in the body and by what mechanism remains only partly identified.
- Whether very weak magnetic fields affect the human body Studies on the health effects of the weak magnetic fields present in everyday environments continue in various countries, and no clear causal link has been established at this point.
In other words, this article, too, describes things "as far as we currently understand them." Magnets may look like a classroom tool, but they remain at the frontier of materials research today.
Links to the textbook (by level)
| Level | Subject / Unit | Where in this article |
|---|---|---|
| JHS | Science ・ Electric current and magnetic fields | The path of force around a magnet, iron-filing patterns |
| HS | Physics ・ Electromagnetism | Magnetic flux density and field strength, the idea of permeability |
| HS+ | Physics ・ Advanced (magnetism) | How alignment forms inside iron, and how heat erases magnet-like behavior |
| Univ. | Electromagnetism ・ Condensed matter physics | Magnetic circuits and shield design, eddy currents |
| Research | Materials science ・ Biophysics | New magnetic materials, animals' magnetic sense |
| ― | Connections to daily life | Fridge notes, storing magnetic cards, handling magnets near precision equipment |
- National Institute for Materials Science (NIMS, 物質・材料研究機構) ― research introduction on magnetic materials
- Magnetics Society of Japan (日本磁気学会), "Magnetic Engineering for Beginners" (初学者のための磁気工学) (fundamentals of magnetic materials and magnetic shielding)
- Feynman, Leighton, Sands, "The Feynman Lectures on Physics III: Electromagnetism" (chapter on magnetic fields and magnetism in matter)
- National Institute of Standards and Technology (NIST) ― explainer on magnetic measurement
※This article is a general-audience science explainer. The figures given are approximations meant to aid understanding of the underlying mechanism. Strong magnets can cause injury, equipment damage, or swallowing accidents. Follow the product's safety instructions when handling them.