Cushioning
Encyclopedia
Package cushioning is used to help protect fragile items during shipment. It is common for a transport package to be dropped, kicked, and impacted: These events may produce potentially damaging shocks. Transportation vibration from conveyors, trucks, railroads, or aircraft can also damage some items. Shock
and vibration
are controlled by cushioning so that the chance of product damage is greatly reduced.
Cushioning is usually inside a shipping container
such as a corrugated box. It is designed to deform or crush to help keep levels of shock and vibration below levels that may damage the product inside the box. Depending on the specific situation, package cushioning can often be between two and three inches thick.
Internal packaging materials (sometimes the same ones used for cushioning) are also used for functions other than cushioning. Some are used just to immobilize the products in the box and to block them in place. Others are just used to fill a void and do not have a cushioning function.
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
foam pieces (Foam peanut
s), similar pieces made of starch-based foams, and common popcorn
. The amount of loose fill material required and the transmitted shock levels vary with the specific type of material.
Paper
-
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. (Mover
s often wrap objects with several layers of Kraft paper
or embossed pulp before putting them into boxes.)
Corrugated fiberboard 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
composite honeycomb structures are also used for cushioning.
Foam
structures -
Several types of polymeric foams are used for cushioning. The most common are: Expanded Polystyrene
(also Styrofoam
), polypropylene
, polyethylene
, and polyurethane
. These can be molded engineered shapes or sheets which are cut and glued into cushion structures.
Foam-in-place is another method of using polyurethane
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
is made from recycled newspapers and is recyclable.
Inflated Products -
Bubble Wrap
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 cushion
s 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, thermoformed end caps, and shock mounts.
, 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, 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.
, or 3) isolate the product from the vibration. Proper design is critical for cushion performance.
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.
Shock (mechanics)
A mechanical or physical shock is a sudden acceleration or deceleration caused, for example, by impact, drop, kick, earthquake, or explosion. Shock is a transient physical excitation....
and vibration
Vibration
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
are controlled by cushioning so that the chance of product damage is greatly reduced.
Cushioning is usually inside a shipping container
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 boxes...
such as a corrugated box. It is designed to deform or crush to help keep levels of shock and vibration below levels that may damage the product inside the box. Depending on the specific situation, package cushioning can often be between two and three inches thick.
Internal packaging materials (sometimes the same ones used for cushioning) are also used for functions other than cushioning. Some are used just to immobilize the products in the box and to block them in place. Others are just used to fill a void and do not have a cushioning function.
Design factors
When designing packaging, the choice of cushioning may depend on many factors:- effective protection of product from shockShock (mechanics)A mechanical or physical shock is a sudden acceleration or deceleration caused, for example, by impact, drop, kick, earthquake, or explosion. Shock is a transient physical excitation....
and vibrationVibrationVibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"... - whether cushioning is resilient (performs for multiple impacts)
- resistance to creep – cushion deformation under static load
- material costs
- labor costs, 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 recyclingRecyclingRecycling is processing used materials into new products to prevent waste of potentially useful materials, reduce the consumption of fresh raw materials, reduce energy usage, reduce air pollution and water pollution by reducing the need for "conventional" waste disposal, and lower greenhouse...
issues - sensitivity of product to static electricityStatic electricityStatic electricity refers to the build-up of electric charge on the surface of objects. The static charges remain on an object until they either bleed off to ground or are quickly neutralized by a discharge. Static electricity can be contrasted with current electricity, which can be delivered...
. - etc.
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
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
foam pieces (Foam peanut
Foam peanut
Foam peanuts, also known as packing peanuts or packing noodles, are a common loose-fill packaging and cushioning material used to prevent damage to fragile objects during shipping. They are shaped to interlock when compressed and free flow when not compressed...
s), similar pieces made of starch-based foams, and common popcorn
Popcorn
Popcorn, or popping corn, is corn which expands from the kernel and puffs up when heated. Corn is able to pop because, like sorghum, quinoa and millet, its kernels have a hard moisture-sealed hull and a dense starchy interior. This allows pressure to build inside the kernel until an explosive...
. The amount of loose fill material required and the transmitted shock levels vary with the specific type of material.
Paper
Paper
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
-
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. (Mover
Moving company
A moving company, removalist, or van line is a company that helps people and businesses relocate their goods from one place to another. Typically they use moving vans, but for international moves or where storage is required, they may use special containerised vans or shipping containers.National...
s often wrap objects with several layers of Kraft paper
Kraft paper
Kraft paper or kraft is paper or paperboard produced from chemical pulp produced in the kraft process.Pulp produced by the kraft process is stronger than that made by other pulping processes; acidic sulfite processes degrade cellulose more, leading to weaker fibers, and mechanical pulping...
or embossed pulp before putting them into boxes.)
Corrugated fiberboard 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
Paperboard is a thick paper based material. While there is no rigid differentiation between paper and paperboard, paperboard is generally thicker than paper. According to ISO standards, paperboard is a paper with a basis weight above 224 g/m2, but there are exceptions. Paperboard can be single...
composite honeycomb structures are also used for cushioning.
Foam
Foam
-Definition:A foam is a substance that is formed by trapping gas in a liquid or solid in a divided form, i.e. by forming gas regions inside liquid regions, leading to different kinds of dispersed media...
structures -
Several types of polymeric foams are used for cushioning. The most common are: Expanded Polystyrene
Polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
(also Styrofoam
Styrofoam
Styrofoam is a trademark of The Dow Chemical Company for closed-cell currently made for thermal insulation and craft applications. In 1941, researchers in Dow's Chemical Physics Lab found a way to make foamed polystyrene...
), polypropylene
Polypropylene
Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...
, polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
, and polyurethane
Polyurethane
A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...
. These can be molded engineered shapes or sheets which are cut and glued into cushion structures.
Foam-in-place is another method of using polyurethane
Polyurethane
A polyurethane is any polymer composed of a chain of organic units joined by carbamate links. Polyurethane polymers are formed through step-growth polymerization, by reacting a monomer with another monomer in the presence of a catalyst.Polyurethanes are...
foams. These fill the box, fully encapsulating the product to immobilize it. It is also used to form engineered structures.
Molded pulp -
Molded pulp
Molded pulp, also named Moulded pulp or Molded Fibre, is a packaging material, typically made from recycled paperboard and/or newsprint. It is used for protective packaging or for food service trays and beverage carriers...
is made from recycled newspapers and is recyclable.
Inflated Products -
Bubble Wrap
Bubble Wrap
Bubble wrap is a pliable transparent plastic material commonly used for packing fragile items. Regularly spaced, protruding air-filled hemispheres provide cushioning for fragile items....
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 cushion
Inflatable air cushion
An inflatable air cushion is a bag of fabric or plastic that can be inflated to provide cushioning. Unlike Bubble Wrap, inflatable air cushions have a check valve to allow the cushion to be inflated or deflated.-History:...
s 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, thermoformed end caps, and 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 engineerPackaging engineering
Packaging engineering, also Package engineering and Packaging Science, is a broad topic ranging from design conceptualization to product placement. All steps along the manufacturing process, and more, must be taken into account in the design of the package for any given product...
, 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, 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.
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 vibration frequency, the cushion May 1) not have any influence on input vibration, 2) amplify the input vibration at resonanceResonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
, or 3) isolate the product from the vibration. Proper design is critical for cushion performance.
Evaluation of finished package
Verification and validationVerification and Validation
In software project management, software testing, and software engineering, verification and validation is the process of checking that a software system meets specifications and that it fulfills its intended purpose...
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
Package testing
Package testing or packaging testing involves the measurement of a characteristic or property involved with packaging. This includes packaging materials, packaging components, primary packages, shipping containers, and unit loads, as well as the associated processes.Testing measures the effects...
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
See also
- Impact forceImpact forceIn mechanics, an impact is a high force or shock applied over a short time period when two or more bodies collide. Such a force or acceleration usually has a greater effect than a lower force applied over a proportionally longer time period of time...
- Packaging and labellingPackaging and labellingPackaging is the science, art, and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of design, evaluation, and production of packages. Packaging can be described as a coordinated system of preparing goods for transport,...
- ShockShock (mechanics)A mechanical or physical shock is a sudden acceleration or deceleration caused, for example, by impact, drop, kick, earthquake, or explosion. Shock is a transient physical excitation....
- VibrationVibrationVibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
- Vibration isolationVibration isolationVibration isolation is the process of isolating an object, such as a piece of equipment, from the source of vibrations.-Passive isolation:Passive vibration isolation systems consist essentially of a mass, spring and damper ....
Further reading
- MIL-HDBK 304C, “Package Cushioning Design”, 1997
- Root, D, “Six-Step Method for Cushioned Package Development”, Lansmont, 1997, http://www.lansmont.com/
- Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6