A simple and effective tent upgrade that adds less than 3g* to the shelter. They are easily installed by looping through the zip and back through the loop of the pull itself forming a simple larks foot knot. And if you're like me and have a, cough, number of tents and shelters then they can easily transfered between them.
I'm not sure whether they are best on the outer side of the fly or on the inside. Or on both!