its regarding the seat matrial, usually soft seated valves have polymer material for seat but its cant stand with high temperatures so you cant use metal seat in like this situations .
You have already got the answers that is possible to give based on the form of your question. If you, however, have a spsecific situation where you have to check sealings on a certain ball-valve, you might get better advice if you open up and describe more details,- as LittleInch tries to tell you in his sub-text.