210 is super strong, lays flat, and is a go-to thread for large flies with heavy materials. Great for spinning deer hair in comparison to GSP thread.... this has a bit of stretch which GSP does not and it can make a difference if you pay attention. This does not cut deer hair with excessive tension like kevlar does, and GSP does too. For big flies, large streamers, tying in large portions of bulky materials, or just an all around very strong and easy to use thread, you can't go wrong with Danville 210