Hello,

I bought some 100nf condensators to use as bypass caps for 7400 series chips. but instead of ceramics i accidentally bought polyester ones. Now i wonder if i can use those aswell?

 

HERE's an old thread that might help you.
Seem's like they're OK.

 

They will work fairly well. They are a bit larger physically, but should do the job of bypassing well enough if you have one per IC. See sigline on bypass caps, there are links which recommend types in order of preference, IIRC.

As long as you didn't buy a reel of them, you'll find plenty of uses for poly film caps in addition to bypass, such as audio circuit coupling/filtering and switch debouncing.