This texture from an ancient time period is certain to incite intrigue.
This could be the perfect envelope if you're in the construction or quarrying industry. With a 135gsm this envelope has some real texture that accompanies the visuals of the envelope well. C5 is likely the ideal size for you has A5 and folded A4 fit perfectly inside without any worries or concerns about dog ears.
You'll be pleased to hear, unique envelopes statistically perform better than plain or white envelopes as they get opened 9x more. With maths on your side there really is no reason not to like this envelope.