Context : Evidence for a spectral flattening of the supernova remnant ( SNR ) HB3 ( G132.7+1.3 ) was recently claimed in literature based on previously published total flux density data , and the flattening was further interpreted as the discovery of thermal bremsstrahlung emission in the shell of HB3 .

Aims : A spectral flattening has never been observed from any SNR before .
Reliable observations of HB3 at frequencies above 3000 MHz are crucial to confirm such a spectral behaviour .

Methods : We extracted 4800 MHz total intensity and polarisation data of HB3 from the Sino-German 6 cm polarisation survey of the Galactic plane made with the Urumqi 25 m telescope , and analysed the spectrum of HB3 , together with Effelsberg data at 1408 MHz and 2675 MHz .

Results : We found an overall spectral index of HB3 of \alpha = -0.61 \pm 0.06 between 1408 MHz and 4800 MHz , similar to the index at lower frequencies .
There is no spectral flattening at high frequencies .
We detected strong polarised emission from HB3 at 4800 MHz .
Our 4800 MHz data show a tangential field orientation in the HB3 shell .

Conclusions :