Here there is some information on thread type and also a deployment test of a stitched seat cover.
http://www.thehogring.com/2012/03/03...ew-this-cover/
Search for Ken, and check also Naseem's reply below, the thread I used was Nylon Size 46 from reading this and a few other posts.
In the test video, of course we only see that it deploys, nobody knows the exact definition of 'proper deployment'. Besides the thread size and type, the frequency of the stitch is as important. Try to get the same spacing between two stitches with the factory to ensure similar deployment characteristics.