Blocking Ports on Ported Speakers

I started playing with putting some pillow cases in the ports of my Pioneer S-1EX speakers. The bass on these is not flabby by any means but I would not say it is super tight either especially in my echoey basement. With the pillow cases in the ports the bass is TIGHT. Too tight actually and very fast. The effect is dramatic. The rest of the frequency range seems to not have been effected. Can anyone recommend where to buy foam ports or similar of varying density to play with? I'm thinking there is a sweet spot with the right density of material whether it be foam or something else.

I know..... I could google it but thought some might have specific recommendations.

Thanks