I had a large gap under my door that let in a draft that I wanted to stop. I installed it at the bottom of the door, face down, and a small strip on the sill, face up, on the edge of the door where the gap widened. It works well for bridging that gap, and I like that it's not a semi-rigid plastic mold like most other options, which I think will break faster in that position. I think the soft felt is enough to stop drafts but is flexible enough to never get in the way when the door is opened and won't become brittle over time.
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