Poplin can shrink but it will depend on the fibers it is made from. If made from polyester then shrinkage may be minimal. But if it is made from silk or cotton there is a strong possibility the material will shrink. The fabric will shrink over time instead of in the wash.

Will poplin shrink?

Tips for Working with Poplin

Avoid using hot water with poplin as it might shrink. Use medium heat when you're ironing poplin. If you're using a steam iron, make sure that you're using the warm setting.

Does poplin shrink in the dryer?

Depending on the fiber content, poplin can be susceptible to heat. A poplin made from 100% cotton could shrink in a hot wash.