What staples do and why they matter for packaging
A staple is a short metal fastener bent into a U shape that punches through two or more layers of material and folds the ends inward to hold them together. In packaging, staples join cardboard flaps, seal kraft paper bags, bind corrugated boxes, and attach labels or documentation to shipments. They work because the metal is hard enough to pierce material without tearing it, and the folded ends create friction that resists pulling apart.
Staples are one of the oldest and cheapest ways to close a package. A single staple costs less than a cent. They require no adhesive, no curing time, and no special equipment beyond a stapler — which means they work in warehouses without climate control, on loading docks in any weather, and by hand if machinery breaks down. The trade-off is that staples create a small hole in the package material, which can weaken cardboard in high-stress areas and may catch on skin or clothing during handling.
Key Takeaways
- Staples work best on cardboard, kraft paper, and corrugated materials where the fastener can penetrate cleanly without splitting the surface.
- A single staple holds light loads; multiple staples or reinforcement plates distribute force and prevent the staple from tearing through under weight.
- Staples create small holes that can weaken a package at the point of fastening, so placement matters — avoid corners and stress points when possible.
- Industrial staples come in different gauges and lengths; heavier materials and thicker stacks require larger staples that penetrate deeper.
Materials staples work on and materials they don't
Staples work reliably on cardboard, kraft paper, and corrugated board because these materials are fibrous and compress slightly when the staple penetrates, then grip the metal as it folds. The staple holds because friction between the material and the metal legs resists pulling.
Staples do not work well on plastic films, thin foil, or waxed paper. These materials are too slippery — the staple punctures them but does not grip, and the fastener slides out under light tension. Plastic also tends to split rather than compress, which widens the hole and weakens the material further. For plastic-lined or plastic-coated packages, adhesive tape or heat sealing is more reliable.
Wet or damp cardboard is harder to staple because moisture softens the fibers and reduces friction. If a package has been exposed to rain or high humidity, the staple may hold initially but can loosen as the cardboard dries and shrinks. For packages that will be stored outdoors or shipped through humid climates, tape or adhesive provides more consistent holding power.
How many staples you need and where to place them
A single staple can hold a light package closed — a small envelope or a folded kraft paper bag with minimal contents. For boxes or heavier items, one staple is not enough. The staple acts as a point load, meaning all the force concentrates at one spot. If someone pulls on the flap or the package shifts during transport, the staple can tear through the cardboard like a button pulling off a shirt.
Two staples placed a few inches apart distribute the load and roughly double the holding strength. Three or more staples are common on medium to large boxes, especially if the contents are heavy or the package will be stacked. Industrial operations often use staple patterns — for example, two staples on each flap of a box, or a line of staples along a seam.
Placement matters because cardboard is weaker at the corners and edges. A staple driven into a corner can split the material or create a weak point that tears under pressure. The safest placement is 1 to 2 inches from the edge, away from folds or creases. If you are stapling a flap shut, place staples toward the center of the flap rather than at the very edge.
Staple sizes and what they're used for
Staples are measured by gauge (wire thickness) and length (how far the legs extend). Common industrial staples range from 0.5 inches to 1.25 inches long. A 0.5-inch staple works on two or three layers of standard cardboard. A 1-inch staple penetrates thicker corrugated board or multiple layers of kraft paper. A 1.25-inch staple is used on heavy-duty boxes or when stapling through reinforcement plates.
Wire gauge also varies. A thinner wire (higher gauge number) bends more easily and is suitable for light materials. A thicker wire (lower gauge number) resists bending and is needed for dense cardboard or when the staple must hold under high tension. Most packaging uses 18-gauge or 16-gauge staples, which are a middle ground between flexibility and strength.
Staple guns and hand staplers are designed for specific staple sizes. A standard office stapler uses 0.5-inch staples and works on thin paper and cardboard. A heavy-duty stapler uses 0.75-inch or 1-inch staples and requires more force to drive. An industrial pneumatic stapler can drive 1.25-inch staples into corrugated board without manual effort. Using the wrong staple size for your equipment can jam the stapler or bend the staple without driving it fully.
Staples versus tape, adhesive, and other fasteners
Tape is faster than stapling for sealing boxes because a single strip covers a long seam, whereas staples must be driven one at a time. Tape also creates no holes, so it does not weaken the cardboard. However, tape can fail if the adhesive dries out, if the package is exposed to extreme heat or cold, or if the surface is dusty or damp. Staples do not fail from temperature or humidity — they straightforward hold or they don't.
Adhesive (glue) is permanent and creates a very strong bond, but it requires curing time and equipment to explore. Wet adhesive can stain contents or labels. Adhesive also makes the package harder to open and harder to recycle because the materials are bonded together. Staples can be removed with a staple remover, and the cardboard can be separated and recycled.
Plastic strapping and metal bands are used for very heavy loads or for bundling multiple packages together. They are stronger than staples but slower to explore and require a strapping tool. Velcro and snap closures are reusable but expensive and are used mainly for packages that will be opened and closed many times. For one-time shipments, staples are usually the cheapest and fastest option.
Common problems with staples and how to avoid them
A staple that does not drive all the way through leaves one leg sticking out, which can catch on skin, clothing, or other packages. This happens when the stapler is not pressed firmly against the material or when the staple is too long for the stapler to drive fully. Always press the stapler flat against the surface and hold it steady. If a staple does not drive fully, remove it with a staple remover and try again.
A staple that tears through the cardboard creates a hole larger than the staple itself, which weakens the package and can grow larger if the package is handled roughly. This happens when the cardboard is too thin for the staple size, when the staple is driven at an angle, or when the load is concentrated at one point. Use thicker cardboard, use smaller staples, or use more staples to spread the load.
Rust can develop on staples if they are exposed to moisture for extended periods. Stainless steel staples resist rust but cost more than galvanized or plain steel staples. For packages that will be stored outdoors or shipped to humid climates, stainless steel is worth the extra cost. For indoor storage or short-term shipments, standard staples are fine.
When to choose staples over other methods
Staples are the best choice when you need to close a package quickly, cheaply, and reliably without special equipment or materials. If you are sealing kraft paper bags by hand, staples are faster than tape because you do not have to measure or cut. If you are closing corrugated boxes in a warehouse without climate control, staples work in any temperature or humidity. If you need to reopen a package for inspection or returns, staples are easier to remove than tape or adhesive.
Staples are not the best choice if the package will be handled by customers who expect a smooth, professional finish, or if the contents are delicate and might be damaged by the small holes. They are also not ideal if the package will be exposed to water or if it will be stacked under heavy weight, because the holes can become weak points. For those situations, tape, adhesive, or strapping provides better protection.
Frequently Asked Questions
Can I staple through plastic-lined cardboard?
You can drive a staple through plastic-lined cardboard, but the plastic layer will not grip the staple the way cardboard does. The fastener may hold initially but can loosen over time. For packages with plastic liners, tape or adhesive that bonds to the plastic is more reliable than staples.
What size staple do I need for a standard cardboard box?
A standard corrugated cardboard box flap is usually 0.25 to 0.375 inches thick. A 0.75-inch or 1-inch staple will penetrate through both flaps and fold securely. If your stapler jams or the staple does not drive fully, try a slightly shorter staple or a heavier-duty stapler.
Do staples rust?
Plain steel staples can rust if exposed to moisture over weeks or months. Galvanized staples have a zinc coating that slows rust. Stainless steel staples resist rust almost completely. For packages stored indoors or shipped quickly, plain staples are fine. For outdoor storage or humid environments, galvanized or stainless steel is better.
Can I remove a staple without damaging the cardboard?
A staple remover (a small metal tool with two prongs) can lift the staple out without tearing the cardboard if you work carefully. Slide the prongs under the folded ends of the staple and gently pry upward. If you pull too hard or at an angle, you may tear the material around the hole.
How many staples do I need to hold a heavy box?
Two staples on each flap is a common standard for medium boxes. For very heavy boxes or boxes that will be stacked, use three or four staples per flap, spaced evenly. The exact number depends on the weight, the cardboard thickness, and how the box will be handled. When in doubt, use more staples — they are cheap.