We so often get asked this question, and it is purely a matter of taste.
The 100% Cashmere Pashminas are softer and squeezier (in the 2ply variety that we sell anyway). They are a little bit fluffier, and have a more open weave.
The 70% Cashmere / 30% Silk Pashminas have a tighter weave and a bit more weight to them. There is a tiny sheen, but they are definately not shiny. The extra weight allows them to hand more elegantly. I would say they feel a tiny bit smoother to stroke.
Here is a close up picture... you can click on it to make it bigger...
One thing to be aware of that it is illegal to say the fibre content of your pashminas is 70% pashmina or 100% pashmina. Sellers that are doing this either don't know what they are doing or are doing something dodgy. The fibre is officially called cashmere. Please see the Cashmere & Camel Hair Institutes website for verification.