When not in use, I keep my bumpfeed thoroughly submerged in dried mud & chlorophyll, and the line lasts. I can trim & edge a quarter acre around the house, patio, driveway, & shed without bumping.
Plastic does NOT absorb water; and even if it's spongy, perforated (weakened) plastic - having water in the hollows won't affect the nature of the plastic. It would only make it heavier, which would cause it to come apart faster. But the first time the head is run up, all the water will sling off anyway.
This thread is VOODOOOOOOOOOOOOOOOOOOOOO.