There are some things that are very influential to so your Curtain looked more natural :
- Cloth material you use. There are a lot of material in 3dsmax cloth curtain that exist, such as spandex, rubber, satin, silk etc.. I suggest you take the time to try out the material one by one and compare the parameters. That way, you will get a material that best matches your needs
- Gravity. Sometimes we have to increase the value of gravity, this way will pull the blinds down so that the curtains don't look too stiff.
- The amount of the segment. The smaller the segment, of course, the object will be more flexible. But do not make it too small segment, because it would burden the 3dsmax file.
3DSMAX Tutorial-Animation AR104- Creating curtain Using Cloth Modifier from azri3d Tutorial on Vimeo.