When the use of a relative term is allowed in a claim, this term is interpreted by the division in the least restrictive possible way when determining the extension of the subject-matter of the claim. As a consequence, in most cases, a relative term is simply not limiting the extension of the subject-matter of a claim.
For example, the expression "a thin metal plate" does not limit the feature "metal plate" against the prior art: a metal plate is "thin" only when compared to another one, but it does not define an objective and measurable thickness. So a metal plate three millimetres thick is thin when compared to a plate five millimetres thick, but thick when compared to a plate one millimetre thick.
As another example, when considering "an element mounted near the end of a truck", is this element mounted 1 mm from the end of the truck, 10 cm or 2 m? The only limitation of such an expression is that the element must be nearer to the end of the truck than to its front, i.e. the element can be mounted anywhere in the second half of the truck.
Also defining a material as "elastic" does not limit the type of material, because elasticity is an intrinsic property of any solid material measured by the module of Young. Therefore an elastic material per se can be anything from rubber to diamond.