The double crochet acts like a mesh material when finished, depending on the thickness of your yarn the double crochet can be see through and drafty.

How to make it:

Make a foundation chain. Yarn over the hook before inserting it into the second chain from where you start, then yarn over again to pull a loop through your foundation. Now you have three loops on your hook. Yarn over and pull through two loops which will leave you with two loops left, then yarn over and pull through the last two loops. Repeat.