Jan van den Hemel writes: In a Sub D modeling workflow where you use a Subdivision modifier to add smoothness to your model, you’ll want to add boundary support wherever you want sharp edges. If you’re not using Creasing, that means adding actual edge loops for support. There’s several methods for adding these loops.
from BlenderNation https://www.blendernation.com/2021/09/11/boundary-protection-for-sub-d-modeling/
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