You should always carry a lens cloth to keep your lens or filter in tip top condition free from rain drops and dust. If not your pictures will suffer from lack of contrast flair and blurred patches.
A microfibre cloth is the best you can use to protect the surface of the lens as you clean, because the cloth is non abrasive. The Tamron cloth comes in a small plastic wallet (11.5x6.5) to keep it clean and measures 14.5cm x8.5cm. Keep one in your gadget bag/back pocket at all times.
If you go out when it's raining - buy two, one for removing the rain, the second as dry cloth to buff the lens and prevent smearing. Take advantage of our offer of four for £10 while stocks last.