Question about CPU Cooling Fan

My computer was having heat problems, so I decided to open her up and take a look and sure enough the cpu cooling fan was covered in dust.

So I removed the Fan and heatsink from the processor to clean it all up.

I noticed a thermal insulator goop, that I tore when removing the heatsink.

Upon some reading I have come to the conclusion that its a good idea to apply some sort of new thermal insulation.

The question is, what on earth can I use? I've looked around the internet and can't find anything that tells me whats ok to use for this...only a bunch of warnings saying I better use something.

So now my heatsink is de-attached from my mother board waiting for me to plug it back in so I can use it

Can someone tell me what I can use and where to get it please?

thank you

You need 'Silver based thermal compound' which you can get from any Electronics store such as Maplin (www.maplin.co.uk).
Costs about £8.

artic silver which is what is mentioned above.

Sorry for late response. But Thank you!
The day after posting the question, I got the answer, and yeah, I went with Arctic Silver....Cooling works fine now