Hint: These are purely man-made fibres. They have no natural counterparts.
Complete answer: We can broadly classify fibres based on their source into natural and synthetic fibres. Well, this classification is very easy to understand but it is very crucial to classifying fibres. This actually forms the first foundation to classify any fibre. Now, as the names suggest, a natural fibre is directly obtained from nature. Obviously, we do not use it as it is. They undergo a very regulated process of purification so as to fit our needs. But they still remain natural fibres as their primary ingredient is directly obtained from nature. Common natural fibres obtained from plant sources are cotton, jute etc. and that from animal sources are silk, wool etc. Synthetic fibres are on the other end of this spectrum. They are completely man-made. Even the primary ingredients that form the foundation of these fibres are artificially produced. Meaning, in no way they have artificial counterparts. Well, in some cases there may be a natural form of the synthetic fibre but there would be many limitations on its use. To tackle this, we make it from scratch in our factories. An example of a synthetic fibre is orlon. It is a type of acrylic fibre which is resistant to high temperatures and chemicals. It is commonly used in automotive industries and also to cover rooftops and in awnings. As it is resistant to moisture it is also used to make raincoats. Other examples include nylon, polyester, spandex, latex, Kevlar etc. Synthetic fibres are often cheaper than natural ones and are also widely available. They are easy to use and do not require much care and attention. But despite this, they pose a serious threat to our environment and their unregulated production can lead to irreparable damages to our surroundings.
Note: Rayon is often considered as a synthetic fibre but this is not the case. Rayon is manufactured from wood pulp. As wood-pulp, which is its primary ingredient, is a naturally obtained substance, rayon is thus classified at best as a semi-synthetic fibre.