What's a skin care system without a serum? Everyone has to have a serum! The Somme Institute Serum is the step after Transport, and it is pretty light in feeling. It sinks into your skin immediately and I didn't notice any residue left behind from it. The serum is a bit hydrating as well, I found it similar to a light moisturizer in hydration level. I had no problems applying makeup over the serum.
The serum has a very high concentration of the MDT5 technology in it, so if you're going to go for any of the products from Somme, I'd start with this one!
Note that the presence of vitamin A in the MDT5 technology means that this entire line should be avoided in pregnancy.