what are the disadvantages of synthetic fibres?
You can take the answer Althaf has provided. However, the first point is a bit ambiguous as it is not always that all synthetic fibres are not comfortable. The rest of the points mentioned by him are perfect.
Good effort! However, it is not always that all synthetic fibres are not comfortable. All other points are absolutely correct.
You can add one more point to these disadvantages. It is that the synthetic fibres catch fire easily. Recall, people usually suggest not to wear nylon clothes in kitchen.
Disadvantage to synthetic fibers is they don't allow your skin to "breath", especialy the ones made from plastics (polyester), it's like wearing a garbage bag. Not only is it uncomfortable but it can have negative health effects because not allowing your skin to breath affects your lymphatic system. Your body uses your skin(which is the largest organ) to eliminate toxins