Transparency in Finland

Here is the last sensation from the Finland post, sold at the single letter rate (0.80 euro, and not more than 3 euros like the lenticulars of France, Austria, and other stamps with heat-activated ink, but I am drivelling).

A Winter transparent stamp. Before, the lenticular stamps picturing ski champions were quite thin.

On this mail received thank to Postcrossing, I can order the postcard to the editor by writing down the barcode. More seriously, the most astucious and artistic-gifted can play with the envelope paper and their pencils to personalise this season's stamp at no cost.

A little worry, from a recent reflexion read on a English-speaking philatelic forum: are not the few plastic stamps issued forbid the recycling of the envelopes on which they are stuck? But it is a very little worry: Who would throw out an envelope without keeping the stamp to himself or for a collector?