Why is the texture of the pasta in a store-bought pasta salad different to the texture of pasta I've cooked at home? So I've bought a store-made pasta salad and I've tried to recreate it at home. 

It consists of Penne and a tomato dressing, fairly simple, however no matter how hard I try I can't emulate the exact texture of the pasta of the store-bought salad. 

At first I thought it was because I overcooked the pasta, but I was pretty certain I didn't. But to be sure I tried several different cooking times on several different batches of the same pasta. To no avail, the texture I am after still eludes me. The texture of the store bought is soft, yet slightly firm and has a pleasant chewiness to it. 

I checked the ingredients on the back of the pasta salad and it says the pasta is made out of Durum Wheat Semolina (and water), this is the same ingredient as the pasta I used is made from. 

So now I am left wondering what the difference in texture could be down to; any ideas?
Expanded from the comments...

Use properly salted water when cooking the pasta.

Slightly undercook the pasta a little bit; the pasta will continue to cook as you prepare the salad.

Do not rinse the pasta.

Mix the ingredients while the pasta are hot; they will absorb more flavour; I would try to season the pasta before adding oil; since oil will tend to coat the pasta and will block the seasoning from being absorbed.

Use a little bit more salt and spices than usual (cold dishes need more "punch".

Good luck and have fun experimenting.