You can wear multiple mining helmets.

[Int0rCess0r]

But only if they appear as a stack, otherwise they act as normal.

[Styg]

Where did you find them stacked?

[harperfan7]

.

[Alt]

stacked helmets are legit, you can do it irl
in infusion each extra helmet should add extra protection from attacks above head

[Vagabond]

stacked helmets are legit, you can do it irl
in infusion each extra helmet should add extra protection from attacks above head

Le COD Warzone stacking several ballistic plates into your carrier plate vest shieeeeet.

[PhrygianDominant]

Fixed for the next patch.

[yako]

Some more non-stackable items you can wear:
4 groin guards (in the room 5 of core city residential underpass)
2 doctor coats (in the room with a doctor in the same area)
3 doctor coats (in the left locker near Anastasia in Fort Apogee)

They can be recycled as a stack, but you will receive the same amount of scraps as if it were a single item.