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The sharing approach is based on a collective circularity principle during the product usage phase. It thus represents a very narrowly defined loop, where circularity is optimized specifically during the usage phase. This approach does not focus on the subsequent recovery of material resources but rather on their ex ante reduction. With the pragmatic insight and foresight that certain products are only temporarily needed within a household, individual ownership becomes unnecessary. By distributing consumption among multiple users, fewer products need to be manufactured, thereby reducing material consumption and contributing to resource conservation and preservation. A key prerequisite for the formation of this loop is ensuring that the shared product is handled with care within the user community. This involves a degree of trust, which can be reinforced through regulations, for example, clarifying procedures for maintenance or repairs when the product requires servicing.

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A prerequisite for this loop is that the user wishing to dispose of a product is willing to make it available to other users for further use. The successful implementation of the loop also depends on the condition and functionality of the product to be reused. This is particularly important, as typically no material interventions are performed by the original user. In other words, any necessary cleaning, maintenance, repair, or refurbishment of the used product becomes the responsibility of the new user.

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Careful handling of products includes, for example, regular cleaning, oiling or greasing of machinery, and proper storage to prevent corrosion. All these measures ensure the quality and durability of the product. It remains intact and is less prone to requiring repairs. Besides careful handling, product design also plays a crucial role in implementing this loop. During the design phase, attention should be given to making the product easy to maintain and overall low-maintenance.

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The need for repair reduces the value of a product. Unlike routine maintenance or servicing, repairs focus on restoration. Partially or fully worn-out or defective components are replaced, thereby reinstating the product’s functionality. A fundamental prerequisite is reparability, meaning that not only must appropriate spare parts be available or be replicable (e.g., via 3D printing), but the product itself must also allow access for repair — i.e., it must be disassemblable. This is not always the case, for example, when product casings are tightly welded together so that access to the internal components is only possible by breaking the casing, which consequently makes repair impossible or economically unfeasible due to cost-benefit considerations. The extent to which usability is impaired due to the need for repair depends on two components.

Firstly, it depends on the degree of functional impairment. This ranges from minor defects that do not fundamentally affect the product’s functionality to damages that result in a complete loss of function and thus render the product unusable.

Secondly, the assessment of the product’s utility also depends on the individual’s perceived level of impairment in usability. For example, some users tolerate the repair needs of a product in the form of wear, chipped, or missing parts and continue to use the product as long as its core function is still intact. Conversely, other users may be disturbed by even minor defects, such as scratches on the product surface, for instance, on a table.

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Restoration involves a more extensive material-technical intervention in a product than simple maintenance or repair. The refurbishment is comprehensive. A damaged object that has become unsightly or unusable in terms of color, shape, or materiality is restored through specialized restoration techniques. This allows the product’s usage phase to be restarted. Synonyms for restoration include reconditioning or overhaul, and colloquially it is sometimes referred to as a complete refurbishment or full renewal. In English usage, the term refurbishing is also occasionally applied. In addition to restoration, measures may be taken to stabilize and prevent future damage (so-called conservation of the object). In any case, restoration must be distinguished from renovation and remediation, as these terms primarily relate to buildings and their upkeep.

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The upcycling loop can be differentiated into various variants. For example, the term remanufacture refers to the incorporation of used product components into the production of a new product with a similar or identical function. In contrast, repurpose denotes the reuse of products or their components to create an entirely different product.

In all cases of upcycling, the focus is on value enhancement, which can be expressed as follows:

1. Creative design through new product concepts (e.g., manufacturing tables from reclaimed wooden planks),

2. Aesthetic appeal (e.g., upcycled objects distinguished by craftsmanship, harmonious form, balanced proportions, and pleasing color compositions),

3. Functional and material innovation (e.g., skillful artisanal integration of old and new product elements, such as embedding digital devices into vintage furniture),

4. Monetary value increase (e.g., driven by the demand of affluent consumers for upcycled products).

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In contrast to upcycling, where materials are transformed into higher-value products, downcycling results in a reduction of the original value and functionality of the material. This is common in cases such as plastics or metals, where the recycled materials do not achieve the same performance or quality as the original material after the cycling process. Although downcycling effectively reduces waste volume, it can lead to a long-term accumulation of lower-quality materials that are more difficult to recycle. A typical example of downcycling is the shredding of PET bottles, where the downcycled plastic often cannot be remanufactured into new bottles but is instead used for lower-value products such as insulation materials.