What does the Wi-Fi signal depend on?

I sit at home with a laptop, the Router is behind two walls, the signal usually goes to 3 sticks and the download speed rarely exceeds 700kbps, usually it holds up at 400-500 (sometimes you have to wear a laptop in the next room, where it takes everything 20MB, but then it caught something 4 sticks and the speed of the torrent 1.2 shows, the laptop did not move, the router, even more so, maybe it depends on the temperature and humidity of the air?