In general when you talk about FLEECE you are talking about the coat of wool that covers a wool-bearing animal, like sheep. On the other hand with WOOL you are talking about the material that is obtained after shearing the fleece.
There are other differences between them acorting to the context.
The Oxford dictionary defines wool as the “fine, soft curly or wavy hair forming the coat of a sheep, goat, or similar animal, especially when shorn and prepared for use in making cloth or yarn”. By this definition, wool is obtained after shearing the fleece. However, American Heritage Dictionary defines wool as “the dense, soft, often curly hair forming the coat of sheep and certain other mammals, such as the goat and alpaca, consisting of cylindrical strands of keratin-covered by minute overlapping scales and much valued as a textile fiber.” The word wool also refers to yarn or textile fibre made from wool.
The word fleece also has multiple meanings. Fleece can refer to the coat of wool covering a wool-bearing animal such as a sheep. It can also refer to the wool obtained from a sheep at one shearing. However, we don’t use the word fleece to refer to wool that has been processed. Neither do we use it to refer to the textile fibre made from wool.
However, fleece can also refer to a type of fabric. Polar fleece is the more accepted term for this fabric. This is soft and warm fabric with a texture similar to wool. It is made from a type of polyester and can be used as a vegan alternative to wool.
Difference Between Fleece and Wool
Fabric:
Fleece is a synthetic fabric made from polyethylene terephthalate.
Wool is a textile fiber obtained from woolen animals. Examples include cashmere, mohair, angora, etc.
Fleece can be used as a vegan substitute for wool since fleece also has many qualities and properties of wool.
Fur of the Animal:
Fleece refers to the woolen coat of an animal.
Wool can refer to fleece which is shorn and prepared for use in making cloth.
However, in general usage, wool can be used interchangeably with fleece to refer to the woollen coat of animals.