why do cheap glue guns take so !@#$^ long to heat up?

 Ever wondered?

 The answer has to do with economics on the one hand (no surprises there) and on the other hand, something called radiative equilibrium.

 We can't just run the heat gun at any old temperature, it has to hit a certain temperature range (≈265º F) and stay there.

 It just isn't economical to add a thermostatic switch or other reactive regulatory mechanism to the heating element on the cheaper guns.

 So the heating element is sized to be just enough to reach the right temperature before radiative equilibrium keeps it from getting hotter. Radiative equilibrium is what happens when an object radiates heat away at the same rate as heat is being put into it.

 Unfortunately, the power level at which this works for these small, hand-held units is so low that warm-up takes a very long time - up to 15min on my last one.

 The 3M unit I just bought must have some kind of temperature regulation (datasheet says "positive temperature coefficient" - a thermistor?) because it has a 250 watt heater, about ten times the power of my last glue gun, and the literature claims it is ready to use in 3 minutes.