How to make something transparent, but not refractive?
To make a material transparent, but not refractive, change its Opacity level instead of its Refraction level.
1. Uniform transparency:
2. Procedural noise in Opacity color slot used to create "cutout" effect:
Note: the "Clip" option next to "Opacity Level" will clip the opacity map to 100% black and 100% white values only. Any smooth gradients (values between black and white) will be ignored. To learn more see: My opacity maps look strange!
If you want to create glass material that does not refract light (like soap bubbles or light bulbs), see: What type of glass should I use?