Strangely, the Pastafarian mythos doesn't seem to support the notion of strainers as religious headgear. The most prominent mention is the colander in the flood myth:
He produced a great Colander of Goodness and He did collect water in
an enormous pot, which He heated; and He did drop in a heaping portion
of pasta and slowly simmer the sauce for so long that the original
human weren't even around anymore when He was finally ready to eat.
And He poured the spaghetti and water into the Colander of Goodness,
careful to make sure that the water went down the drain of His sink.
And as He was eating, He vacantly considered where the drain did
empty, and the FSM said, "Uh oh."
Source: The Gospel of the Flying Spaghetti Monster - The Flood
And no part of this story implies that wearing the great colander would be a particularly good thing.
Even the Loose Canon has no more than a passing mention of someone wearing a "Holy Colander" and one Pastalm mentioning a strainer. So, it seems as though strainers are worn by Pastafarians solely because they're pasta-related and hemispherical.
However, there is a completely different kind of outfit that the mythos is extremely supportive of: Pirate regalia.
... it is disrespectful to teach our beliefs without wearing His
chosen outfit, which, of course, is full Pirate regalia.
Source: The Gospel of the Flying Spaghetti Monster - Pamphlets
There is no single reason why pirate regalia has this status, but the Gospel has a lot to say about pirates in general. Here are a few memorable examples:
Pirates, as you know, are His Chosen People. Yet their numbers have
been shrinking ever since the 1800s. Consequently, we find that global
warming, earthquakes, hurricanes, and other natural disasters are a
direct result of the shrinking number of Pirates.
Source: The Gospel of the Flying Spaghetti Monster - The Spaghedeity
... we were created in His ideal image: that of the Pirate. Since then
we've only come to resemble other people's gods. ... It is important that we return to the ways of the Pirate before it's too
Source: The Gospel of the Flying Spaghetti Monster - Unified Spaghetti Cheory