The most common and most likely answer to this crossword clue is the 6 letter word TOWELS
I've seen this crossword clue in The Times
T
O
W
E
L
S
More clues leading to the result TOWELS
Buddy explains!

The straight part
We know that "They dry" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they dry = towels.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TOWELS mean?
TOWELS noun- A cloth used for wiping, especially one used for drying anything wet, as a person after a bath.
- To hit with a towel.
- To dry by using a towel.
- To block up (a door, etc.) with a towel, to conceal the fumes of a recreational drug.
- To beat with a stick.