Package cushioning is used to protect items during

shipment Freight transport, also referred to as freight forwarding, is the physical process of transporting commodities and merchandise goods and cargo. The term shipping originally referred to transport by sea but in American English, it has been exte ...

Vibration Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...

and impact shock during shipment and loading/unloading are controlled by cushioning to reduce the chance of product damage. Cushioning is usually inside a

shipping container A shipping container is a container with strength suitable to withstand shipment, storage, and handling. Shipping containers range from large reusable steel boxes used for intermodal shipments to the ubiquitous corrugated box design, corrugated b ...

such as a

corrugated box Corrugated box design is the process of matching design factors for corrugated fiberboard (sometimes called corrugated cardboard) or corrugated plastic boxes with the functional physical, processing and end-use requirements. Packaging engineers w ...

. It is designed to absorb shock by crushing and deforming, and to dampen vibration, rather than transmitting the shock and vibration to the protected item. Depending on the specific situation, package cushioning is often between thick. Internal packaging materials are also used for functions other than cushioning, such as to immobilize the products in the box and lock them in place, or to fill a void.

Design factors

When designing

packaging Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a coo ...

the choice of cushioning depends on many factors, including but not limited to: * effective protection of product from shock and

vibration Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...

* resilience (whether it performs for multiple impacts) * resistance to creep – cushion deformation under static load * material costs * labor costs and productivity * effects of temperature, humidity, and air pressure on cushioning * cleanliness of cushioning (dust, insects, etc.) * effect on size of external shipping container * environmental and

recycling Recycling is the process of converting waste materials into new materials and objects. This concept often includes the recovery of energy from waste materials. The recyclability of a material depends on its ability to reacquire the propert ...

issues * sensitivity of product to

static electricity Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it can move away by an electric current or electrical discharge. The word "static" is used to differentiate it from electric ...

Common types of cushioning

;Loose fill: Some cushion products are flowable and are packed loosely around the items in the box. The box is closed to tighten the pack. This includes expanded

polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It i ...

foam pieces ( foam peanuts), similar pieces made of starch-based foams, and common

popcorn Popcorn (also called popped corn, popcorns, or pop-corn) is a variety of corn kernel which expands and puffs up when heated. The term also refers to the snack food produced by the expansion. It is one of the oldest snacks, with evidence of p ...

. The amount of loose fill material required and the transmitted shock levels vary with the specific type of material. ;

Paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses, Feces#Other uses, herbivore dung, or other vegetable sources in water. Once the water is dra ...

: Paper can be manually or mechanically wadded up and used as a cushioning material. Heavier grades of paper provide more weight-bearing ability than old newspapers. Creped cellulose wadding is also available. Movers often wrap objects with several layers of kraft paper or embossed pulp before putting them into boxes. ;

Corrugated fiberboard Corrugated fiberboard, corrugated cardboard, or corrugated is a type of packaging material consisting of a fluted corrugated sheet and one or two flat linerboards. It is made on "flute lamination machines" or "corrugators" and is used for maki ...

pads: Multi-layer or cut-and-folded shapes of corrugated board can be used as cushions. These structures are designed to crush and deform under shock stress and provide some degree of cushioning.

Paperboard Paperboard is a thick paper-based material. While there is no rigid differentiation between paper and paperboard, paperboard is generally thicker (usually over 0.30 mm, 0.012 in, or 12 Inch#Equivalents, points) than paper and has certain superior ...

composite honeycomb structures are also used for cushioning. ;

Foam Foams are two-phase materials science, material systems where a gas is dispersed in a second, non-gaseous material, specifically, in which gas cells are enclosed by a distinct liquid or solid material. Note, this source focuses only on liquid ...

structures: Several types of

polymeric foam A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

s are used for cushioning, the most common being expanded polystyrene,

polypropylene Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer Propene, propylene. Polypropylene belongs to the group of polyolefin ...

polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bott ...

, and

polyurethane Polyurethane (; often abbreviated PUR and PU) is a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane term ...

. These can be molded engineered shapes or sheets which are cut and glued into cushion structures. Convoluted (or ''finger'') foams are sometimes used. Some degradable foams are also available. Foam-in-place is another method of using

foams. These fill the box, fully encapsulating the product to immobilize it. It is also used to form engineered structures. ;Molded pulp: Pulp can be molded into shapes suitable for cushioning and for immobilizing products in a package.

Molded pulp Molded pulp or molded fiber (also spelled as moulded pulp or moulded fibre) is a packaging material, that is typically made from recycled paperboard and/or newsprint. It is used for protective packaging or for food service trays and beverag ...

is made from recycled

newsprint Newsprint is a low-cost, non-archival paper consisting mainly of wood pulp and most commonly used to print newspapers and other publications and advertising material. Invented in 1844 by Charles Fenerty of Nova Scotia, Canada, it usually has ...

and is recyclable. ;Inflated products:

Bubble wrap Bubble wrap is a pliable transparency (optics), transparent plastic material commonly used for protecting fragile items during shipping. Known for its cushioning air-filled bubbles, it has also become a cultural icon, celebrated for its satisfy ...

consists of sheets of plastic film with enclosed “bubbles” of air. These sheets can be layered or wrapped around items to be shipped. A variety of engineered inflatable air cushions are also available. Note that inflated air pillows used for ''void-fill'' are not suited for cushioning. ;Other: Several other types of cushioning are available including suspension cushions, biofoams, thermoformed end caps,

viscoelastic In materials science and continuum mechanics, viscoelasticity is the property of materials that exhibit both Viscosity, viscous and Elasticity (physics), elastic characteristics when undergoing deformation (engineering), deformation. Viscous mate ...

materials, and various types of shock mounts.

Design for shock protection

Proper performance of cushioning is dependent on its proper design and use. It is often best to use a trained packaging engineer, reputable vendor, consultant, or independent laboratory. An engineer needs to know the severity of shock (drop height, etc.) to protect against. This can be based on an existing

specification A specification often refers to a set of documented requirements to be satisfied by a material, design, product, or service. A specification is often a type of technical standard. There are different types of technical or engineering specificati ...

, published industry standards and publications, field studies, etc. Knowledge of the product to be packaged is critical. Field experience may indicate the types of damage previously experienced. Laboratory analysis can help quantify the fragility of the item, often reported in g's. Engineering judgment can also be an excellent starting point. Sometimes a product can be made more rugged or can be supported to make it less susceptible to breakage. The amount of shock transmitted by a particular cushioning material is largely dependent on the thickness of the cushion, the drop height, and the load-bearing area of the cushion (static loading). A cushion must deform under shock for it to function. If a product is on a large load-bearing area, the cushion may not deform and will not cushion the shock. If the load-bearing area is too small, the product may “bottom out” during a shock; the shock is not cushioned. Engineers use “cushion curves” to choose the best thickness and load-bearing area for a cushioning material. Often two to three inches (50 – 75 mm) of cushioning are needed to protect fragile items. Computer simulations and

finite element analysis Finite element method (FEM) is a popular method for numerically solving differential equations arising in engineering and mathematical models, mathematical modeling. Typical problem areas of interest include the traditional fields of structural ...

are also being used. Some correlations to laboratory drop tests have been successful. Cushion design requires care to prevent shock amplification caused by the cushioned shock pulse duration being close to the

natural frequency Natural frequency, measured in terms of '' eigenfrequency'', is the rate at which an oscillatory system tends to oscillate in the absence of disturbance. A foundational example pertains to simple harmonic oscillators, such as an idealized spring ...

of the cushioned item.

Design for vibration protection

The process for vibration protection (or isolation) involves similar considerations as that for shock. Cushions can be thought of as performing like springs. Depending on cushion thickness and load-bearing area and on the forcing vibration frequency, the cushion may 1) not have any influence on input vibration, 2) amplify the input vibration at

resonance Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration whose frequency matches a resonant frequency (or resonance frequency) of the system, defined as a frequency that generates a maximu ...

, or 3) isolate the product from the vibration. Proper design is critical for cushion performance.

Evaluation of finished package

Verification and validation Verification and validation (also abbreviated as V&V) are independent procedures that are used together for checking that a product, service, or system meets requirements and specification (technical standard), specifications and that it fulf ...

of prototype designs are required. The design of a package and its cushioning is often an iterative process involving several designs, evaluations, redesigns, etc. Several (ASTM, ISTA, and others) published package testing protocols are available to evaluate the performance of a proposed package. Field performance should be monitored for feedback into the design process.

ASTM Standards

* D1596 Standard Test Method for Dynamic Shock Cushioning Characteristics of Packaging Material * D2221 Standard Test Method for Creep Properties of Package Cushioning Materials * D3332 Standard Test Methods for Mechanical-Shock Fragility of Products, Using Shock Machines * D3580 Standard Test Methods for Vibration (Vertical Linear Motion) Test of Products * D4168 Standard Test Methods for Transmitted Shock Characteristics of Foam-in-Place Cushioning Materials * D4169 Standard Practice for Performance Testing of Shipping Containers and Systems * D6198 Standard Guide for Transport Packaging Design * D6537 Standard Practice for Instrumented Package Shock Testing For Determination of Package Performance * and others

Notes

External links

Institute of Packaging Professionals

International Safe Transit Association

Westpak webinar on protective packaging
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