Re: low reynolds number...
I would imagine there is a mass/volume threshold when any object first strikes a significant density of gas, would tend to heat or slow down. Since both processes involve the exchange of kinetic energy for heating (and with ablation as mentioned) which produces braking.
So ISS velocity is 7660 m/s , kinetic energy of something feather like (4 g say)= 1/2 x 0.004 * 7660^2= 117kJ
Change in Temp = Total energy in/(mass * specific heat)
deltaT=(117x10^3)/(0.004*1700) = 17257 K.
Charred feather assuming it took a few minutes? Probably pieces... (assuming 1700 J/kg.K specific heat for generic protein and negligible radiation).
This of course, is a maximum based solely on kinetic energy conversion, but atmospheric interactions play a large part. Specifically the Space Shuttle tiles ride a pressure wave that creates a plasma to dissipate the energy.
You can see NASA approved numbers here .
This back of envelope calculation highlights just how amazing space vehicle re-entry engineering is, since it is clearly a very hostile environment!!