No idea what this means! [closed]

Solution 1:

To rephrase:

Some applications fit this description: "relatively non-thermally critical structural parts are required.". That is, they require "relatively non-thermally critical structural parts", which means "structural parts" which are "relatively non-thermally critical", which at a guess would mean that the structural parts function well over a relatively wide range of temperatures.

The things referred to as "they" (the polymers) are limited to these applications, because of the thing referred to as "this" (something to do with a variation in temperature perhaps).

The whole thing could perhaps be rephrased as "You can only use these polymers in situations where the temperature isn't going to vary widely".

Does that help?

Solution 2:

The meaning is likely to be ...

They may only be used where, in comparison to other parts that must remain stable and safe when hot, their susceptibility to heat does not matter.

In this suggestion I have retained the proper meaning of “relative” (some sort of comparison) and have not taken it to mean “rather” or “quite”. This point has been ignored in all comments and other answers.

The obscurity of the original is such that I would not employ the writer to make a user manual or a safety guide!