Instant Screen Door

From the website:

Lets fresh air in, keeps bugs out!

Screen attaches to almost any door frame with Velcro strips (included).

Perfect for homes, apartments, campers.

Fits doors up to 80" high x 36" wide.

Has cloth handles and weighted bottom.

81-1/2" x 36-1/2".

$12.98 here.

Note: not recommended for use as a shower curtain — unless you're hacking the Water Door.