Somewhere on teh intarwebs Jeff Layman wrote:
solaara wrote:
I have found a way to get my propagator to work even better...I have
a 2" thick piece of polystyrene under it so more heat is generated
upwards towards the pots...has anyone else thought of this...?

If the propagator temperature isn't thermostatically controlled, you
may find that by using polystyrene its temperature gets too high on
warm days, as there will be very little if any heat loss throught he
base. That could do more harm than good.

If, as you say, there will be very little heat loss through the base then it
follows that there will be very little (reflected lost) heat *gain* through
the base as well. Therefore your argument is null.
--
Shaun.

"Build a man a fire, and he`ll be warm for a day. Set a man on fire, and
he`ll be warm for the rest of his life." Terry Pratchett, Jingo.