Your macarons will stick to the silicone mat if they are undercooked.
Bake your macarons for 1-2 minutes longer than when using parchment paper for the macarons to be easily peeled from the silicone baking mat.
Macarons are not fully cooled
Macarons will stick to the silicone baking mat if haven’t fully cooled before trying to remove them. Let them cool for at least 20 minutes before trying to remove the macarons. Usually it’s easier to leave the macarons on the baking sheet and let the macarons cool on the silicone baking mat for at least 20 minutes. Then peel the macarons off of the silicone baking mat and fill them.
Silicone baking mat is oily
Silicone baking mats cannot have any oily residue, or particulate present on the baking mat when using them for macarons. The macarons will absorb the oil while baking, making the macarons very difficult to get off of the silicone baking mat.
To remove oily residue from the silicone baking mat, wash it with soap and water and rinse to let dry.
If the oily residue is still present, pour boiling water on the silicone baking mat and it will clean the baking mat perfectly to use for your macarons.
Baking pan is old
Macarons need fresh aluminum baking pans to cook well. If your baking pan is old, unfortunately the macarons will stick to silicone and even parchment paper. Macarons need the conductivity of aluminum to cook evenly and for the temperature to be evenly distributed while baking. Use a new aluminum baking pan for cooking macarons if your pans are quite well used.
Baking pan is oily
Macarons will absorb any oil that’s present on the baking pan through the silicone or parchment paper. Remove any oily residue from the pan by washing it with soap and water.
If the baking pan will not become clean after using soap and water, pour boiling water on the baking pan. The boiling water will clean the baking pan to remove any oil that is present and make it freshly clean to use for baking macarons on.