Yes it is. Why? Because in doing so you are deliberately encouraging thoughts of fornication and adultery and turning sexuality, God's precious gift to a married couple, into a commodity which demeans those participating in it.
Matthew 5:28But I say to you that every one who looks at a woman lustfully has already committed adultery with her in his heart.
That applies to women as well as men. You cannot indulge in pornography without encouraging lust. To do that is sinful.
I hope you have found this helpful.