Fillings may be loose, prepared, sprung, or elastomeric (see Figure 3.9). Loose fillings are supplied as an amorphous mass which requires encasing between layers of other materials, for example cloth stretched over the fill and tacked to the frame. They may require to be teased into position and stitched to take and retain the desired shape. Prepared fillings have already been given a form, either by machine or by hand. They may consist of one or more layers ready for use, requiring only to be cut and attached to the frame. The selection of fillings is guided by price, comfort and durability. These in turn are influenced by factors such as density, resilience, ease of use and the amount of training required to use them properly.
The quality of filling is often judged and graded by its resilience, that is, its ability to recover its size and shape after deformation, especially after compression. Loose fillings require skill and judgement in handling and are therefore expensive to use. Prepared fillings have an economic advantage over loose fillings in that they may be cut to size and less skill is required to use the materials, both in judging quantities and in applications.
A common characteristic of loose fillings is that they are highly compressed for shipping and transportation. Therefore, they require opening out before use. This may be a manual or mechanical process. Different terminology is used for different grades of filling in different countries and there is no agreed international standard.
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