In reply to waterbaby:
The "clever" way is to use iron on tape but fit it reversed inside, will need to fold and then open up once pushed through tear, like a ship in a bottle. A few small stiches to hold the tear together and then iron on to set. It once worked for me for a small tear. And once did not with the result I had to make the tear worse to remove my mess to then take it into the market to get it done properly.
If you can get at a seam inside the jacket unpick a bit and seam grip tear together on the inside and reinforce with thin tape, I did that with another jacket.
Finally I had Rab repair a tear in the sleeve of a Rab Extreme down jacket, and invisible it is not. They sewed it then sewed a square patch on top, but its nice and strong.
You might have noticed a bit of a theme to my carelessness.