Iterative design process

An iterative design process is a circular or cyclic way of designing in which ideas are repeatedly researched, developed, modelled, tested and evaluated. Designers move backwards and forwards through the process rather than following one fixed sequence. Each cycle should use new evidence to improve the design.

Iterative design cycle

Research → Ideate → Prototype → Test → ↺ repeat and refine

Why iteration is used

A designer rarely knows the optimum solution at the start. Research, modelling and testing can reveal problems that were not obvious during initial idea generation. The designer can then return to the relevant stage, investigate the problem and modify the proposal.

For example, testing a power drill may show that the handle is uncomfortable. This leads to further research into handle ergonomics, followed by a modified handle. That change may require a different switch, so the designer then researches switches and refines the design again. If ventilation testing shows that the motor requires larger vents, the casing or handle may also need to change. One modification can therefore create another cycle of research, modelling and evaluation.

Research within an iterative process

Research should continue throughout development rather than being completed only at the beginning. Designers can use:

questionnaires and surveys to investigate users, interests and buying habits
interviews with potential users to identify needs and wants
focus groups to obtain qualitative feedback from potential customers
observation and empathic research, where designers experience or simulate user limitations
product analysis and disassembly to identify useful features and construction methods
practical testing of materials, components, construction methods and finishes
anthropometric data and ergonomic observation to improve fit, comfort and usability
secondary research into materials, components, manufacturing methods, designers, movements and relevant anthropometric data.

The value of research depends on whether it affects the design. Evidence should lead to a decision, modification or further investigation rather than simply being collected.

Developing a design proposal

A proposal is gradually refined through sketches, models, testing and feedback. Development can include:

Sketching and modelling possible solutions to the design problem.
Checking ideas against specification criteria using critical and evaluative annotations.
Using client or potential-customer feedback to select a proposal for further development.
Refining the aesthetics and overall form of the chosen proposal.
Carrying out tests and trials to develop details such as size, proportion, materials and construction.
Using scale, full-size or functioning models where appropriate to evaluate the design with clients, users and production specialists.
Modifying the proposal in response to the evidence gathered.
Producing dimensioned working drawings with sufficient information for manufacture once the design is resolved.

Evaluation throughout development

Evaluation is not only a final check. Designers should continually compare ideas and prototypes with the specification and with evidence from users and testing. A successful iteration explains what was learned, what changed and why the change improves the design.

The cycle continues until the proposal meets the relevant user needs, specification requirements and manufacturing constraints as effectively as possible.