Quote from Chilius03 on October 29, 2013, 5:51 pm

In portal, there are some certain setting you want to watch for, i can tell you them all

DirectX level

In portal, there is a graphics card setting known as DirectX levels, These DirectX levels can be changed without graphics card properties using this common trick

mat_dxlevel (numbers)

here are the possible numbers

70
81
85
91
95

These numbers will alter the game's portals and graphics affects, Portal does have affect on Non-portable walls.

(an example of DX9 portals)

(an example of DX8 and DX7 portals)

EDIT:I was asked this, someone has suggested about the E3 Portals from 2006.
They are DirectX 9.5 as asked, if you are making a portal mod, add this to description "RECOMMEND DIRECTX 9.5 FOR BEST PORTALS"