Hulled barley, also known as barley groats, is the whole grain form of barley, with only the outermost hull removed. Chewy and rich in fiber, it's the healthiest kind of barley. However, it takes longer to cook than pearl barley, about an hour or more.
Pearl barley is the most common form of barley. It's still chewy and nutritious, but less so than hulled barley because the outer husk and bran layers have been removed. The polished grains are also softer and take less time to cook, about 40 minutes.
Most recipes call for pearl barley or intend for cooks to use this type even if they don't specify. However, it is usually fine to substitute hulled barley. Just be aware that you may need to adjust the recipe cooking time.
Here are a few recipes from the Kitchn archives:
Related: Good Question: How Do I Cook Barley?
(Image: Emily Ho)