Nicely-coloured and small freeze blocks. Please note that they are not refillable so you cannot fill them with water yourself - even though there is a 'lid' at the top. They are filled with gel-type freezable material and the lid does not come off. The 100 ml size means that these should comply with airline safety restrictions of liquids/gels being stored in no more than 100 ml containers. Disclaimer: I haven't tried these on a plane yet!
Update: I used these on a trip by aeroplane now (to help keep my lunch cold) and they were fine. I took them out at security and included them with my creams/cosmetics etc for inspection. All went well, the size is within the 100ml limit.