What is the difference between linen and cotton canvas?
From Understanding the difference canvas and linen:


  Canvas can mean different things to different people. In the context of painting, the word ‘canvas’ means a fabric used as a painting surface. The difference is that sometimes the canvas is made from cotton fibres and other times from linen fibres. Each material is worth looking at in more detail.
  
  Cotton
  
  Cotton is a soft, fluffy fibers that grows in a boll or protective capsule around the seeds of cotton plants. The plant is native to the Americas, Africa and India and is most often spun into yarn or thread to create a soft, breathable textile - the chances are you are wearing some cotton right now.
  
  The advantage of cotton to you as an artist is that it is affordable and it stretches very easily. A properly prepared cotton canvas will last a long time and is the most popular surface for oil and acrylic painting, especially for students, although it is considered too flexible for very large paintings. It is classified according to its weight and surface texture.
  
  When it comes to tightness, cotton comes out on top. It is possible to stretch cotton tighter than linen without straining the wooden support around the canvas, and a heavy-grade cotton can make up for its lack of strength and weight.
  
  Linen
  
  Linen is strong and durable, and remains the preferred surface for many artists but it is expensive. It is made from the fibers of the flax plant and top quality flax is harvested mainly in Western Europe. If you want your painting to last then a linen canvas is a sound investment. The threads that make up linen, known as the warp and weft threads, weigh the same, which means they are less prone to expansion or contraction due to moisture. 
  
  Linen retains its natural oils, which helps to preserve the fibre’s flexibility and stops the canvas from going brittle. It is also regarded as having a more ‘natural’ weaved finish than cotton – a variety of textures and weights are available in both rough and smooth finishes.
  
  Because of its strength linen holds up to a heavy painting hand and does not become slack as easily as cotton canvas."