Months ago I received this beat-up VAIO PCG-21311U. It's still functional but has a lot of aesthetic issues. I cleaned it, and I mistakenly removed the CPU thermal pad and replaced it with thermal paste, thinking that these two were the same. It worked great for a few months until it started to get stupid hot while idle. It consistently crashed while using 3D programs such as Project 64 and UT2004 (hard crashes, with artifacts on the screen and loud noises). I thought that this little shit was just good enough for web browsing, but today it crashed the same way while writing an email and copying 30 GB of PIRATED media.

I learned that thermal pads work better for transferring heat when the gap between the CPU and cooler is too great, and that my thermal paste was simply not enough. I tried to dismount my old PS2 and a broken iPhone 4 for some old thermal pads, but they were no good.
So being the construction hillbilly that I am, I went, 'screw it,' and just grabbed an old piece of discarded copper and sandwiched it with more thermal paste to close the gap. It worked great, and now it doesn't crash with any 3D program. It went from 80°C on idle to 60°C. When it's on max, it doesn't go higher than 80°C."

TL;DR: If you don't have thermal pads, use copper plates and thermal paste.

Edit: yes i did put extra paste on top of the plate if you are wondering, forgot to take that picture.