"Extra firmness" means that something is very stiff or rigid, making it harder to bend or compress.
Sentences with «extra firmness»
That, no doubt, has been at least partially responsible for a little extra firmness in the Canadian dollar not just across the U.S. dollar but across a wider range of currency. (sencanada.ca)
The breathe - flex ™ is a dual firmness design with extra firmness for proper development on the infant side and extra comfort on the toddler side thanks to additional Flex - PE ™ foam layers. (colgatekids.com)
They provide extra firmness, durability, and strong side and edge support so a mattress won't sag when your baby stands or walks near the edge. (consumerreports.org)