Closure options

Generally speaking you have two different options:
You either use cotton ribbons (holds up to high washing temperatures better) or elastic which is easier to use.
If you are making a mask for somebody with a disability (or think arthrits in their hands or shoulders) tying a ribbon is probably very hard and painful. Small children will probably have a hard time too.

I would recommend using elastic (unless you plan to use the masks daily), because it's more practical and unassuming! It's super easy to change the elastic if it happens to become limp anyway :)

BTW - a mask is no excuse to ignore social distancing! So don't fall victim to a false sense of security!

Option 1: Ribbons

Just thread a ribbon through each side

Use a safety pin to make your life easier (a bobby pin will work too, but is a bit harsher for your ribbon)

The ribbons get tied behind your back

Option 1.1. instead of using 2 ribbons use 1 long ribbon instead (ommit one of the knots in the picture above for a continious piece of ribbon)

Option 2: Elastic

Two loops for your ears 

My favourite option: one continious loop behind your head

I'm sure there are a lot of other options, those are just the 4 that I could think of of the top of my head. If you happen to think of different materials or other ways to tie them etc. Please comment below :)