What is the difference between ultrathin, layered

The above is the correct text of the example with the underlining. The issue in this sentence is not that of the ultra-thin, layered or ultrathin and layered because they are not underlined.

However, there is more grammar than that in this issue. Some series of adjectives are called coordinate adjectives, if they all modify a single noun – just as in this case– ultrathin, layered - both adjectives modifying the noun construction. Such coordinate adjectives can also be correctly used along with an and in between them without distorting the meaning. If there are more than two adjectives, as usual the last adjective will take the and before. Because they all equally modify the single noun, even if you reverse the order, the meaning will not suffer.
So ultrathin, layered and ultrathin and layered are both usable equitably. There is no difference

hey daagh, can we get the options as well?

Also, I don't remember coming across this concept of coordinate adjectives...is this something I need to look out for on SC?

just Google around, you will get it.
Whether coordinate adjectives are required for GMAT or not, it is better to know it

Great daagh ... kudos to you

Here 's an excerpt from https://englishplus.com/grammar/00000072.htm

There is a two-part test for coordinate adjectives:
(1) Can you replace the comma with the word and?
(2) Can you reverse the order of the adjectives and keep the same meaning?