During the 1800s what the worlds most valuable fur pelt? why?

Beaver pels were the most important because they were good for insulation on hats and clothes.

Beaver fur, which was used in Europe to make felt hats, became the most valuable of these furs. The fur trade prospered until the mid-1800's, when fur-bearing animals became scarce and silk hats became more popular than felt hats made with beaver.