This is a remix of a flexi track, basically just two joined together so it's 21cm long when contracted. It's design allows you to bend the track enabling easier connections to Trackmaster tracks that are not forgiving. Do note that the trains will not go around as sharp a turn as you can flex the track.  

I've printed this on PLA. 

You may need to scrape the bottom of the connectors to ensure they are smooth so that it's able to connect