Thank you for your letter of December 24, 1973 (reference number ML-1228).

     I would like to pass along for your consideration a variation of the balloon-decoy idea.  It is that instead of using balloons, it might be possible to use foam.  The ideas are similar in that in both cases, a low-volume, low-mass package rapidly expands to produce a large but low-density decoy; the chief difference being that a balloon is a single space enclosed by a solid whereas foam is many spaces each enclosed by a liquid.

     Optimally, the foam would have heat and radar characteristics that would attract a missile, but foam might have an additional advantage which I think of as "spitting in the missile's eye."  That is, the foam could be chosen so that if penetrated by a missile (or by a pursuing airplane), it would cover the missile with a film that was opaque to heat and radar, thereby blinding the missile.  A secondary advantage might be that unlike the balloon, foam can disappear in a few minutes leaving nothing for the enemy to retrieve and examine.

     I am enclosing a photocopy of an advertisement for foams that appeared in the September, 1973 issue of Scientific American, from which it appears that a wide variety of foams has already been developed.