Packaging design influences the end user’s perception of the packaging and also has an impact on the functionality. Therefore the design should clearly tell the end user how to use and open the product. A small change in the design can have a great impact on the end user’s possibility to transfer force in the opening process. Therefore the packaging design has to be compared to the force needed to open the packaging (see test your packaging).


Design has an influence on the possibilities for transfer of force

Cold cuts trays:

Studies of the flap size on cold cuts packaging have shown that by increasing the flap size from 1×1 cm to 2×2 cm you make it possible to transfer more force in the opening situation. In practice it means that 50% of a person’s finger strength can be used instead of only 25%. This is partly due to the fact that a larger contact space between finger and flap provides a better grip (see choice of materials), and partly due to the fact that the grip you are able to apply to a larger flap holds more force; Pincer grip instead of key grip (see opening grips).


Furthermore many end uses – especially men – complain that you need long finger nails in order to separate the two layers of foil before you are able to pull the flaps. A small knob in the bottom layer of foil can make this easier

Screw caps:

In order to open the round screw cap your hand has to grip hard enough to create enough friction force to be able to turn at the same time, that is to create a momentum strong enough to open the cap. Unfortunately many types of packaging are often a bit flexible and thereby the great pressure from the grip presses the packaging into an oval shape (see below). This induces the need for an even greater momentum in order to open. Measurements show that the momentum increase is 10-30%. This can be helped by using a different material for the packaging (see choice of materials) or by using another design, e.g. a lid with wings or edges in order to reduce the friction.




Udformning af skruelåg


The choice of material for many types of packaging influences the design thereby requiring more force to open.


Size matters

The screw cap size implies how much force you are able to transfer in the opening situation. Testing persons with no physical ailments show that the larger the diameter the more force they are able to transfer. Of course this is only true to a certain size as it depends on the end user’s hand size.


On an average men in England has a hand breadth of 10.7 cm and a hand length of 19 cm while women’s hands are respectively 9.2 cm and 17.5 cm. As you can see in the figure below the difference in hand size greatly influences the possibilities for transferring force. Even though men are stronger than women the women are almost able to transfer the same amount of force as men when opening small screw caps (diameter less than 45 mm). Men on the contrary can use their strength better on screw caps with a diameter of more than 65 mm.


A study has proven that a screw cap of 75 mm is the size where most people can transfer the greatest force but at the same time this cap size results in great abrasion of the finger joints especially when the hands are small. Therefore a screw cap with a smaller diameter is to be preferred.


Besides the turning strength by opening a packaging with screw cap the grip strength and fine motor skills are also important to consider (see physical force).


Wrist twisting strength – women

Transfer of force (Nm), women for different dimensions of screw caps 20 mm – 85 mm in diameter (click the picture to get a larger version).



Wrist twisting strength – men

Transfer of force (Nm), men for different dimensions of screw caps 20 mm – 85 mm in diameter  (click the picture to get a larger version).








Useful advice on packaging design

  • The larger the screw cap diameter the more force can be transferred.
  • The larger the grip space the more force can be transferred.
  • A more powerful grip on a packaging can be obtained if the packaging has edges instead of being round.
  • The opening procedure can be made more intuitive by making physical changes in the design.
  • Choice of materials can support the design – e.g. by having grooves in the packaging (see choice of materials).
  • Always test a new packaging design on your target group (see end user observations – this is how you do).


Good design can guide the end user to easy opening

Design is part of the visual impression of the packaging and together with the graphics it holds great importance for how the packaging is perceived.


The cold cuts tray can be improved by marking the opening with two side cuts making the opening mechanism obvious. In a study this change meant that 94% of the healthy persons and 82% of the elderly and handicapped with reduced strength were able to open as compared to respectively 33% and 18% who were able to open the traditional packaging with no side cuts.


(Reference: Development project focusing on retail packaging accessibility, Main parts A & B, R&D Centre for Assistive Technology and Hjælpemidler og Rehabilitation, Danish Tecnological Institute and Center for Accessibility, 1999).


A certain challenge can make some end users avoid the packaging based on previous experience. This is especially true for the types of packaging that require a lot of strength to open (pull rings in cans or tins), or types of packaging which are heavy and those breaking or wasting the product in the opening process. Therefore it is important to study potential barriers when changing to a new design.