Internal stiffener material on German M43 field cap visors

Here are two well-used original M43 field caps. Authentication of these hats in general has become difficult for me but both of these came from  highly regarded dealers more than 10 years ago and were positively reviewed on WAF; I am extremely confident in stating that these are original wartime Wehrmacht field caps.

Both of these have cardboard internal stiffeners inside the visors. Through wear and use, the cardboard has broken up/crumbled and become very soft and pliable. It can be bent into any shape desired and will not hold its shape, returning to a generally flat, floppy, droopy position.

One of these caps has some insect damage to the underside of the visor, revealing some of this cardboard in the brim. It is a light tan color.

The typical coarse, loose texture of this type of wool is also noticeable here.