  We developed a model for wind-blown bubbles with temperature and density
profiles based on self-similar solutions including thermal conduction. We
constructed also heat-conduction bubbles with chemical discontinuities. The
X-ray emission is computed using the well-documented CHIANTI code (v6.0.1).
These bubble models are used to (re)analyse the high-resolution X-ray spectrum
of the hot bubble of BD+30{\deg}3639, and they appeared to be much superior to
constant temperature approaches.
  We found for the X-ray emission of BD+30{\deg}3639 that temperature-sensitive
and abundance-sensitive line ratios computed on the basis of heat-conducting
wind-blown bubbles and with abundances as found in the stellar photosphere/wind
can only be reconciled with the observations if the hot bubble of
BD+30{\deg}3639 is chemically stratified, i.e. if it contains also a small mass
fraction ($\simeq$ 3 %) of hydrogen-rich matter immediately behind the
conduction front. Neon appears to be strongly enriched, with a mass fraction of
at least about 0.06.
