Change all materials then return the old materials?

I have figured out how to change all of the materials in my game at the same time using

     if(Input.GetKeyDown("3"))
     {
         for(int i = 0 ; i < environ.Length ; i++)
         {
             rend[i] = environ[i].GetComponent<Renderer>();
             rend[i].material.shader = echo;
             rend[i].material = EchoMaterial;
         }

With echo and EchoMaterial being shaders and materials. But I cannot figure out a way to store all of the game objects current material at the start of the game, so that at another push of a button the materials return to what they were before. Is there a way to assign all of the materials to an array or something so that they can all be returned? Or do I have to go through every individual game object and set a variable to be its old material and then manually assign each one?