All the helms in the books seem to be illustrated like armor. When a character without armor proficiency wears a magic helm, does he suffer the same penalties as if he wore other armor? In the DMG, the illustration makes helms appear armored.
Helms are not Armor
Helms are considered wondrous items and thus neither benefit your armor class nor require proficiency with any kind of armor.
2\$\begingroup\$ You may want to add that they also don't contribute to AC. \$\endgroup\$– GreySageJan 28, 2017 at 0:27
3\$\begingroup\$ You also might want to revise to say "helm", since none of the items use the word helmet. It probably doesn't make a tremendous amount of difference, but we might as well make sure to use the given terms. \$\endgroup\$ Jan 28, 2017 at 0:41
1\$\begingroup\$ I was not aware of the difference between helms and helmets. TIL. Fixed. \$\endgroup\$– ThyzerJan 28, 2017 at 0:54
1\$\begingroup\$ It would be good to refer to the armor table and note the absence of helms or helmets as separate items on that table. p 145 phb \$\endgroup\$ Jan 28, 2017 at 2:07
1\$\begingroup\$ @KorvinStarmast except full plate does include a helmet. It's not a separate item, like you say, but it would interfere with using both a helm and full plate and it is an example of helmet-that-is-armor. \$\endgroup\$– nitsua60 ♦Jan 28, 2017 at 4:05