I must to embroider a logo on a sweatshirt made in polar. Which needle ? Stabilizer , and every advice will be welcome. Thank you in advance for your kindness !

Check the amount of stitches in the design and stabilize accordingly.
Always use iron on tear away stabilizer on the back. Then slip the appropriate number of medium weight tear away stabilizers under the hoop.You might need 2 or 3 layers depending on the density, and remembering that the design may not have been digitized for fleecy of stretch knit fabrics.
I am not sure what you call polar fleece in the States or in Europe, but if it is normal fleecy for windcheaters or sweatshirts you do not need wss stabilizer on top. If it has a pile,or is fluffy, then you do.
A no.11 needle is fine. If you have a Janome use the blue tipped.

Françoise, as Lucy said - use two layers of WSS topping on the top of your poplar fleece and a good tear away stabilizer for your backing - you should have a beautiful stitch out - it will be lovely! *4U

I EMBROIDER ON POLAR FLEESE ALL THE TIME.REGULAR NEEDLE(KNITS) FOR YOUR MACHINE,I USE WATER SOLUABLE STABLIZER ON TOP(I-2) LAYERS SO THE STICHES DONT SINK INTO THE FLEESE TO MUCH.ON THE BACK I SUSE TAREAWAY.THEN IF YOU WONT IRON ON A SOFT THIN LYER OF STABLIZER THEY USE ON BABYS CLOTHES,DONT KNOW THE NAME I BOUGHT IT A DICK SICK SITE.. LUCY