Complex sentence: Unlike overcoats, topcoats are usually made from lighter weight cloth such as gabardine or covert, while overcoats are made from heavier cloth or fur, because overcoats are more commonly used in winter when warmth is more important.
Split into simpler sentences: Unlike overcoats, topcoats are usually made from lighter weight cloth such as gabardine or covert, while overcoats are made from heavier cloth or fur. This is because overcoats are more commonly used in winter so warmth is more important.