through the UV, and in some cases, even in the X-ray (e.g., @pottasch84 [@z89; @st01; @corradi03; @schoen05; @sandin08; @sahai11; @chanplans; @gdm13]). Investigations using far-infrared (far-IR) radiation are especially critical to comprehend PNs as complex physical systems in their entirety, because a large fraction of the nebula mass may reside outside the central ionized region (e.g., @villaver02). For example, up to about 4M$_{\odot}$ of matter has been found in the far-IR halo of [@ueta06; @vanhoof13]. However, according to the recent mass budget estimates based on the UV to mid-IR photometric survey of the Magellanic Clouds, the amount of circumstellar dust grains has been severely underestimated: only about 3% of the ISM dust grains is accounted for in the warm component of the circumstellar envelopes [@matsuura09; @boyer12]. What this implies is that the most extended cold regions of the circumstellar envelope could contain this “missing mass” component, which can only be detected in the wavelength ranges in the far-IR and longer.

Recent opportunities provided by the [*Spitzer Space Telescope*]{} ([*Spitzer*]{}; @werner04), [*AKARI Infrared Astronomy Satellite*]{} ([*AKARI*]{}; @murakami07), and [*Herschel Space Observatory*]{} ([*Herschel*]{}; @pilbratt10) have made it possible to probe the very extended, coldest parts of PN haloes at the highest spatial resolutions 