Both, fabric and the pattern. Actually, there is nothing new sewing-wise on this top, but the combination just works perfectly.
The fabric is a rest of eyelet cotton I used for this dress, underlined with lightweight silk. The pattern is Simplicity 6808, again already used here and here.
I was planning to sew a top from this eyelet for a long time, I just needed some underlining, as I did not have much left from the original dress (and anyhow, the dress underlining was ecru, not perfectly white).
Again I used my special underlining method (at least I have not heard about it elsewhere) where I sew the fabric and underlining together on all seams with the tiny seam allowance put inside. I do this on all direct seams, of course, the armscyes or hems are left apart or simply sewn together. Here is an example of a prepared piece before construction.
Of course, this technique requires a tested pattern and no fitting issues as there simply is no possibility for that. Once your pattern pieces are ready, you sew them up and do not ask many questions anymore. I think it gives nicer finish and less bulk on the seams than hongkong finish or any other seam binding.
I could use a decorative zip on the side and did bias binding on all hems.
So this is the final result, clearly, a white top was missing in my wardrobe and I like this one a lot.