These materials are called forest fibers, as they are made of regenerated cellulose where the raw materials comes from wood chips, spruce and pine birch and eucalyptus. The forest fiber can shrink in laundry as well as natural materials in general. The great thing is, that much of the shrinkage is easily recovered by gently stretching the fabric in the wet state and brushing it with steam. Moisten the garment with for exemple a water spray before ironing!