It is not possible to blow the filter out of the funnel. The harder you blow, the more strongly is the filter drawn into the funnel. This can be explained by Bernoulli's law, according to which the pressure in a stream of air is lowered where the stream is narrower. Therefore the pressure is lowered in the narrow gap between the paper filter and the glass funnel, and the pressure of the air from outside holds the filter in the funnel.