Help can tearablecloth be like egg membrane？

[superbad714]

Other than using the automatic force-based tearing (which doesn't allow you to choose which edges are torn, these are selected based on a force threshold) you can call the cloth's Tear(StructuralConstraint edge) method manually on edges of your choice, which makes the shape  of the torn area entirely up to you.

Note that after calling Tear() one or more times, you must call cloth.UpdateDeformableTriangles(); to update the cloth's visual representation.

Thanks, it helps me a lot, for an older post, I learn that distance lterations and substeps control elastic of cloth. in real practice, I  drag cloth at a random point, with I release drag, the cloth won't recover to its original form, it just keeps popping up at the drag point. How can I preserve this situation? 
Any reply will be appreciated!