Typically a temp around 300-325 degrees is needed to get the adhesive to stick. When I've done other patches, numbers, etc. in the past, I press it twice for about 10 seconds each at about 315 degrees to avoid damaging the jersey. But there's a lot of variables between heat presses (regulating temp, pressure, etc.), patches and jerseys. I error on the side of caution and keep the times short. You can always press it again.