Yes, grease proof paper. To be frank, I have no clue how old that tech is, and what they did before that. Of course, there were no hobby bushcrafters thrn, but the travelling people and Armed Forces must have wrapped their food in something?? I have falled for the ‘environment frirndly BS many, many times. But I am one of those nerds that like to fig in books ( and Internet) to discover the bare truth. It is disappointing usually. I am a true Optimist, but sadly, a deep Pessimist about our future. Just so you know, there will be a new kind of ‘plastic’ anslog on the market soon, there has bern a breakthrough in Sweden how to synthesize Ethyl ( I think it was) efficiently and (fairly) cheaply, which will make it possible to make a similar material to plastics from cellulose. Of course it will be still more expensive than oil based plastic, so poorer countries will continue flooding the World with it....... I think that the most environmentally friendly thing is to buy a quality product and use it for as long as you can. Be it plastic or Tin. Buy Tuppenware and use it for the next 40 years. That is all good!